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/api_repo_files_change_test.go

@@ -93,7 +93,7 @@ func TestAPIChangeFiles(t *testing.T) {
 				req := NewRequestWithJSON(t, "POST", fmt.Sprintf("/api/v1/repos/%s/%s/contents", user2.Name, repo1.Name), &changeFilesOptions).
 					AddTokenAuth(token2)
 				resp := MakeRequest(t, req, http.StatusCreated)
-				gitRepo, _ := git.OpenRepository(repo1)
+				gitRepo, _ := git.OpenRepository(t.Context(), repo1)
 				defer gitRepo.Close()
 				commitID, _ := gitRepo.GetBranchCommitID(t.Context(), changeFilesOptions.NewBranchName)
 				createLasCommit, _ := gitRepo.GetCommitByPath(t.Context(), createTreePath)