Check for sha256 support to use --object-format flag (#28928)

This should fix https://github.com/go-gitea/gitea/issues/28927

Technically older versions of Git would support this flag as well, but
per https://github.com/go-gitea/gitea/pull/28466 that's the version
where using it (object-format=sha256) left "experimental" state.

`sha1` is (currently) the default, so older clients should be unaffected
in either case.

Signed-off-by: jolheiser <john.olheiser@gmail.com>

modules/git/repo.go

@@ -101,7 +101,9 @@ func InitRepository(ctx context.Context, repoPath string, bare bool, objectForma
 	if !IsValidObjectFormat(objectFormatName) {
 		return fmt.Errorf("invalid object format: %s", objectFormatName)
 	}
-	cmd.AddOptionValues("--object-format", objectFormatName)
+	if SupportHashSha256 {
+		cmd.AddOptionValues("--object-format", objectFormatName)
+	}
 
 	if bare {
 		cmd.AddArguments("--bare")