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)

tests/integration/git_push_test.go

@@ -205,7 +205,7 @@ func runTestGitPush(t *testing.T, u *url.URL, gitOperation func(t *testing.T, gi
 
 	doGitAddRemote(gitPath, "origin", u)(t)
 
-	gitRepo, err := git.OpenRepositoryLocal(gitPath)
+	gitRepo, err := git.OpenRepositoryLocal(t.Context(), gitPath)
 	require.NoError(t, err)
 	defer gitRepo.Close()