Test git-annex symlink-based repos

[kousu]

git-annex's original design stored symlinks for all its annexed files, but recently they started defaulting to "unlocked" files -- meaning, files having their full contents on disk in place -- by adding a .gitattributes file that sets up git-annex smudge as a git filter. But there are cases where symlinks still show up -- all repos on https://github.com/OpenNeuroDatasets for example, or if you git annex init and git-annex decides your filesystem is "crippled" (i.e. doesn't have symlinks)). See https://git-annex.branchable.com/tips/unlocked_files/ and even https://git-annex.branchable.com/git-annex-adjust/ for more).

The current tests test for the "unlocked" case:

gitea/integrations/git_annex_test.go

Lines 755 to 768 in de51980

	f, err := os.Create(path.Join(repoPath, ".gitattributes"))
	if err != nil {
	return err
	}
	_, err = f.WriteString("* annex.largefiles=nothing")
	if err != nil {
	return err
	}
	_, err = f.WriteString("*.bin filter=annex annex.largefiles=anything")
	if err != nil {
	return err
	}
	f.Close()

We should test the "locked" case as well.

[kousu]

This was covered in #20