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_file_create_test.go

@@ -153,7 +153,7 @@ func TestAPICreateFile(t *testing.T) {
 			req := NewRequestWithJSON(t, "POST", fmt.Sprintf("/api/v1/repos/%s/%s/contents/%s", user2.Name, repo1.Name, treePath), &createFileOptions).
 				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(), createFileOptions.NewBranchName)
 			lastCommit, _ := gitRepo.GetCommitByPath(t.Context(), treePath)
@@ -276,7 +276,7 @@ func TestAPICreateFile(t *testing.T) {
 			AddTokenAuth(token2)
 		resp = MakeRequest(t, req, http.StatusCreated)
 		emptyRepo := unittest.AssertExistsAndLoadBean(t, &repo_model.Repository{OwnerName: "user2", Name: "empty-repo"}) // public repo
-		gitRepo, _ := git.OpenRepository(emptyRepo)
+		gitRepo, _ := git.OpenRepository(t.Context(), emptyRepo)
 		defer gitRepo.Close()
 		commitID, _ := gitRepo.GetBranchCommitID(t.Context(), createFileOptions.NewBranchName)
 		latestCommit, _ := gitRepo.GetCommitByPath(t.Context(), treePath)