Fix Actions being enabled accidentally (#24802)

[GiteaBot]

Backport #24802 by @wolfogre

Regression of #24536. If the user doesn't explicitly disable Actions, it will be enabled.

1. Gitea will call loadRepositoryFrom before loadActionsFrom.
   

   gitea/modules/setting/setting.go

   Lines 234 to 237 in 25d4f95

   	loadRepositoryFrom(cfg)
   	loadPictureFrom(cfg)
   	loadPackagesFrom(cfg)
   	loadActionsFrom(cfg)

2. In loadRepositoryFrom, rootCfg.Section("actions").Key("ENABLED").MustBool(true) will set actions.ENABLED with true.
   

   gitea/modules/setting/repository.go

   Lines 313 to 315 in 25d4f95

   	if !rootCfg.Section("actions").Key("ENABLED").MustBool(true) {
   	Repository.DisabledRepoUnits = append(Repository.DisabledRepoUnits, "repo.actions")
   	}

3. In loadActionsFrom, rootCfg.Section("actions") will get a section with Actions enabled.
   

   gitea/modules/setting/actions.go

   Lines 23 to 26 in 25d4f95

   	sec := rootCfg.Section("actions")
   	if err := sec.MapTo(&Actions); err != nil {
   	log.Fatal("Failed to map Actions settings: %v", err)
   	}

Although the cause of the problem was using true by copy-paste mistake, it also surprised me that rootCfg.Section("actions").Key("ENABLED").MustBool(true) doesn't only read, but also write.