Do not create commit graph for temporary repos (#23219) (#23302)

Backport #23219

When fetching remotes for conflict checking, skip unnecessary and
potentially slow writing of commit graphs.

In a test with the Blender repository, this reduces conflict checking
time for one pull request from about 2s to 0.1s.

---------

Signed-off-by: Andrew Thornton <art27@cantab.net>
Co-authored-by: Brecht Van Lommel <brecht@blender.org>

services/pull/temp_repo.go

@@ -68,6 +68,12 @@ func createTemporaryRepo(ctx context.Context, pr *issues_model.PullRequest) (str
 	remoteRepoName := "head_repo"
 	baseBranch := "base"
 
+	fetchArgs := []git.CmdArg{"--no-tags"}
+	if git.CheckGitVersionAtLeast("2.25.0") == nil {
+		// Writing the commit graph can be slow and is not needed here
+		fetchArgs = append(fetchArgs, "--no-write-commit-graph")
+	}
+
 	// Add head repo remote.
 	addCacheRepo := func(staging, cache string) error {
 		p := filepath.Join(staging, ".git", "objects", "info", "alternates")
@@ -109,7 +115,7 @@ func createTemporaryRepo(ctx context.Context, pr *issues_model.PullRequest) (str
 	outbuf.Reset()
 	errbuf.Reset()
 
-	if err := git.NewCommand(ctx, "fetch", "origin", "--no-tags").AddDashesAndList(pr.BaseBranch+":"+baseBranch, pr.BaseBranch+":original_"+baseBranch).
+	if err := git.NewCommand(ctx, "fetch", "origin").AddArguments(fetchArgs...).AddDashesAndList(pr.BaseBranch+":"+baseBranch, pr.BaseBranch+":original_"+baseBranch).
 		Run(&git.RunOpts{
 			Dir:    tmpBasePath,
 			Stdout: &outbuf,
@@ -172,7 +178,7 @@ func createTemporaryRepo(ctx context.Context, pr *issues_model.PullRequest) (str
 	} else {
 		headBranch = pr.GetGitRefName()
 	}
-	if err := git.NewCommand(ctx, "fetch", "--no-tags").AddDynamicArguments(remoteRepoName, headBranch+":"+trackingBranch).
+	if err := git.NewCommand(ctx, "fetch").AddArguments(fetchArgs...).AddDynamicArguments(remoteRepoName, headBranch+":"+trackingBranch).
 		Run(&git.RunOpts{
 			Dir:    tmpBasePath,
 			Stdout: &outbuf,