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/editor_test.go

@@ -220,7 +220,7 @@ func testEditorWebGitCommitEmail(t *testing.T) {
 	require.True(t, user.KeepEmailPrivate)
 
 	repo1 := unittest.AssertExistsAndLoadBean(t, &repo_model.Repository{ID: 1})
-	gitRepo, _ := git.OpenRepository(repo1)
+	gitRepo, _ := git.OpenRepository(t.Context(), repo1)
 	defer gitRepo.Close()
 	getLastCommit := func(t *testing.T) *git.Commit {
 		c, err := gitRepo.GetBranchCommit(t.Context(), "master")