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_get_test.go

@@ -42,7 +42,7 @@ func TestAPIGetRequestedFiles(t *testing.T) {
 	session = loginUser(t, user4.Name)
 	token4 := getTokenForLoggedInUser(t, session, auth_model.AccessTokenScopeWriteRepository)
 
-	gitRepo, err := git.OpenRepository(repo1)
+	gitRepo, err := git.OpenRepository(t.Context(), repo1)
 	assert.NoError(t, err)
 	defer gitRepo.Close()
 	lastCommit, _ := gitRepo.GetCommitByPath(t.Context(), "README.md")