chore: still keep ctx in git.Repository struct for cat-file batch command (#38684)

Unfortunately, we can't completely remove the ctx from git.Repository,
because the CatFileBatch still heavily depends on a parent context.

If we remove the Repository ctx, the CatFileBatch will become a mess and
create a lot of unnecessary git processes.

http://localhost:3000/-/admin/monitor/perftrace

* Before: open a repo home, dozens of git processes (duplicate cat-file)
* After: only a few (no duplicate cat-file)

services/actions/scoped_workflow_cache.go

@@ -50,7 +50,7 @@ func LoadParsedScopedWorkflows(ctx context.Context, sourceRepo *repo_model.Repos
 	}
 
 	// cache miss: open the source repo at the exact SHA we keyed on
-	sourceGitRepo, err := git.OpenRepository(sourceRepo)
+	sourceGitRepo, err := git.OpenRepository(ctx, sourceRepo)
 	if err != nil {
 		return "", nil, fmt.Errorf("open source repo: %w", err)
 	}