Refactor `git.HomeDir` to strict mode (report fatal when it's not initialized correctly)

[wxiaoguang]

At the moment, it's impossible to make the git.HomeDir work in strict mode, for unknown reasons (ref: #19930)

If git.HomeDir calls log.Fatal when it's not initialized, some integration tests fails.
https://drone.gitea.io/go-gitea/gitea/55939/3/7

This problem should be fixed in new PRs, to make sure git module always be initialized correctly.

=== TestRepoLanguages (integrations/git_helper_for_declarative_test.go:95)
--- FAIL: TestRepoLanguages (1.65s)
    testlogger.go:78: 2022/06/11 04:50:14 ...eb/routing/logger.go:99:func1() [I] [62a41f06-15] router: completed GET /user2/repo1/_new/master/ for , 200 OK in 46.9ms @ repo/editor.go:184(repo.NewFile)
    testlogger.go:78: 2022/06/11 04:50:14 ...eb/routing/logger.go:99:func1() [I] [62a41f06-27] router: completed POST /api/internal/hook/pre-receive/user2/repo1 for 127.0.0.1:57948, 200 OK in 7.8ms @ private/hook_pre_receive.go:106(private.HookPreReceive)
    testlogger.go:78: 2022/06/11 04:50:14 ...eb/routing/logger.go:99:func1() [I] [62a41f06-17] router: completed POST /user2/repo1/_new/master/ for , 303 See Other in 401.9ms @ repo/editor.go:344(repo.NewFilePost)
    testlogger.go:78: 2022/06/11 04:50:15 ...eb/routing/logger.go:99:func1() [I] [62a41f07] router: completed GET /api/v1/repos/user2/repo1/languages for , 200 OK in 6.5ms @ repo/language.go:48(repo.GetLanguages)
    api_repo_languages_test.go:48: 
        	Error Trace:	api_repo_languages_test.go:48
        	            				git_helper_for_declarative_test.go:96
        	            				git_helper_for_declarative_test.go:91
        	            				git_helper_for_declarative_test.go:95
        	            				api_repo_languages_test.go:17
        	Error:      	Arguments must have the same number of keys
        	Test:       	TestRepoLanguages

        --- FAIL: TestGit/HTTP/PushCreate (1.29s)
            testlogger.go:78: 2022/06/11 04:54:05 ...eb/routing/logger.go:99:func1() [I] [62a41fed-8] router: completed GET /user2/repo-tmp-push-create-http.git/info/refs?service=git-receive-pack for 127.0.0.1:58168, 401 Unauthorized in 3.9ms @ repo/http.go:531(repo.GetInfoRefs)
            testlogger.go:78: 2022/06/11 04:54:05 ...eb/routing/logger.go:99:func1() [I] [62a41fed-9] router: completed GET /user2/repo-tmp-push-create-http.git/info/refs?service=git-receive-pack for 127.0.0.1:58168, 403 Forbidden in 200.4ms @ repo/http.go:531(repo.GetInfoRefs)
            testlogger.go:78: 2022/06/11 04:54:05 ...eb/routing/logger.go:99:func1() [I] [62a41fed-11] router: completed GET /user2/repo-tmp-push-create-http.git/info/refs?service=git-upload-pack for 127.0.0.1:58170, 401 Unauthorized in 3.5ms @ repo/http.go:531(repo.GetInfoRefs)
            testlogger.go:78: 2022/06/11 04:54:06 ...eb/routing/logger.go:99:func1() [I] [62a41fed-12] router: completed GET /user2/repo-tmp-push-create-http.git/info/refs?service=git-upload-pack for 127.0.0.1:58170, 404 Not Found in 200.4ms @ repo/http.go:531(repo.GetInfoRefs)
            testlogger.go:78: 2022/06/11 04:54:06 ...eb/routing/logger.go:99:func1() [I] [62a41fee-2] router: completed GET /user2/repo-tmp-push-create-http.git/info/refs?service=git-receive-pack for 127.0.0.1:58172, 401 Unauthorized in 3.8ms @ repo/http.go:531(repo.GetInfoRefs)
            testlogger.go:78: 2022/06/11 04:54:06 ...eb/routing/logger.go:99:func1() [I] [62a41fee-3] router: completed GET /user2/repo-tmp-push-create-http.git/info/refs?service=git-receive-pack for 127.0.0.1:58172, 200 OK in 209.2ms @ repo/http.go:531(repo.GetInfoRefs)
            testlogger.go:78: 2022/06/11 04:54:06 ...eb/routing/logger.go:99:func1() [I] [62a41fee-11] router: completed POST /api/internal/hook/pre-receive/user2/repo-tmp-push-create-http for 127.0.0.1:58174, 200 OK in 8.0ms @ private/hook_pre_receive.go:106(private.HookPreReceive)
            testlogger.go:78: 2022/06/11 04:54:06 ...eb/routing/logger.go:99:func1() [I] [62a41fee-6] router: completed POST /user2/repo-tmp-push-create-http.git/git-receive-pack for 127.0.0.1:58172, 200 OK in 573.4ms @ repo/http.go:499(repo.ServiceReceivePack)
            git_test.go:595: 
                	Error Trace:	git_test.go:595
                	Error:      	Should be false
                	Test:       	TestGit/HTTP/PushCreate

--- FAIL: TestPullMerge (2.69s)
    testlogger.go:78: 2022/06/11 04:57:31 ...eb/routing/logger.go:99:func1() [I] router: completed POST /user2/repo1/pulls/6/merge for , 303 See Other in 613.0ms @ repo/pull.go:885(repo.MergePullRequest)
    pull_merge_test.go:86: 
        	Error Trace:	pull_merge_test.go:86
        	            				git_helper_for_declarative_test.go:96
        	            				git_helper_for_declarative_test.go:91
        	            				git_helper_for_declarative_test.go:95
        	            				pull_merge_test.go:69

        	Error:      	"[%!s(*webhook.HookTask=&{1 1 1 uuid1 <nil>   true 0 1970-01-01 00:00:00 UTC false  <nil>  <nil>})]" should have 2 item(s), but has 1
        	Test:       	TestPullMerge

--- FAIL: TestPullRebase (2.70s)

    testlogger.go:78: 2022/06/11 04:57:31 ...es/pull/temp_repo.go:117:createTemporaryRepo() [E] [62a420bb-47] Unable to fetch origin base branch [user2/repo1:master -> base, original_base in /drone/src/integrations/gitea-integration-sqlite/data/integrations/gitea-integration-sqlite/tmp/local-repo/pull.git169687650]: exit status 128:

        	fatal: '/tmp/tmp.zvcOK53rAu/integrations/gitea-integration-sqlite/gitea-repositories/user2/repo1.git' does not appear to be a git repository
        	fatal: Could not read from remote repository.

        	Please make sure you have the correct access rights
        	and the repository exists.

    testlogger.go:78: 2022/06/11 04:57:31 ...rvices/pull/patch.go:64:TestPatch() [E] [62a420bb-47] CreateTemporaryPath: Unable to fetch origin base branch [user2/repo1:master -> base, original_base in tmpBasePath]: exit status 128

        	fatal: '/tmp/tmp.zvcOK53rAu/integrations/gitea-integration-sqlite/gitea-repositories/user2/repo1.git' does not appear to be a git repository
        	fatal: Could not read from remote repository.

        	Please make sure you have the correct access rights
        	and the repository exists.

    testlogger.go:78: 2022/06/11 04:57:31 ...rvices/pull/check.go:341:testPR() [E] testPatch[2]: Unable to fetch origin base branch [user2/repo1:master -> base, original_base in tmpBasePath]: exit status 128

        	fatal: '/tmp/tmp.zvcOK53rAu/integrations/gitea-integration-sqlite/gitea-repositories/user2/repo1.git' does not appear to be a git repository
        	fatal: Could not read from remote repository.

        	Please make sure you have the correct access rights
        	and the repository exists.

--- FAIL: TestPushDeployKeyOnEmptyRepo (8.13s)
   testlogger.go:78: 2022/06/11 04:58:50 ...eb/routing/logger.go:99:func1() [I] [62a4210a-11] router: completed GET /api/v1/repos/user2/deploy-key-empty-repo-1?token=037da467132d3d8120015afa8fad0f5d505cfcf1 for , 200 OK in 209.3ms @ repo/repo.go:502(repo.Get)
    --- FAIL: TestPushDeployKeyOnEmptyRepo/CheckIsNotEmpty (0.21s)
        ssh_key_test.go:25: 
            	Error Trace:	ssh_key_test.go:25
            	            				api_helper_for_declarative_test.go:146
            	Error:      	Not equal: 
            	            	expected: false
            	            	actual  : true
            	Test:       	TestPushDeployKeyOnEmptyRepo/CheckIsNotEmpty

[wxiaoguang]

FIXED!

The problem is in gitea post-receive hook, which calls git.NewCommand before git.Init. The failure message is not shown in CI logs, it's really difficult to debug ......