python3Packages.google_cloud_pubsub: disable tests

tests fail due to file handle issues, then just loops
in an invalid state until timing out on hydra

https://hydra.nixos.org/build/129081889

pkgs/development/python-modules/google_cloud_pubsub/default.nix

@@ -20,10 +20,14 @@ buildPythonPackage rec {
   checkInputs = [ pytest mock ];
   propagatedBuildInputs = [ enum34 grpc_google_iam_v1 google_api_core ];
 
+  # tests don't clean up file descriptors correctly
+  doCheck = false;
   checkPhase = ''
     pytest tests/unit
   '';
 
+  pythonImportsCheck = [ "google.cloud.pubsub" ];
+
   meta = with stdenv.lib; {
     description = "Google Cloud Pub/Sub API client library";
     homepage = "https://github.com/GoogleCloudPlatform/google-cloud-python";