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_general_test.go

@@ -811,7 +811,7 @@ func doCreateAgitFlowPull(dstPath string, ctx *APITestContext, headBranch string
 			return
 		}
 
-		gitRepo, err := git.OpenRepositoryLocal(dstPath)
+		gitRepo, err := git.OpenRepositoryLocal(t.Context(), dstPath)
 		require.NoError(t, err)
 
 		defer gitRepo.Close()