chore: fail samples nox session if python version is missing (#17)

Author: gcf-owl-bot[bot]

.github/.OwlBot.lock.yaml

@@ -1,17 +1,3 @@
-# Copyright 2021 Google LLC
-#
-# Licensed under the Apache License, Version 2.0 (the "License");
-# you may not use this file except in compliance with the License.
-# You may obtain a copy of the License at
-#
-#     http://www.apache.org/licenses/LICENSE-2.0
-#
-# Unless required by applicable law or agreed to in writing, software
-# distributed under the License is distributed on an "AS IS" BASIS,
-# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
-# See the License for the specific language governing permissions and
-# limitations under the License.
-
 docker:
   image: gcr.io/cloud-devrel-public-resources/owlbot-python:latest
-  digest: sha256:a3a85c2e0b3293068e47b1635b178f7e3d3845f2cfb8722de6713d4bbafdcd1d
+  digest: sha256:82b12321da4446a73cb11bcb6812fbec8c105abda3946d46e6394e5fbfb64c0f

samples/snippets/noxfile.py

@@ -98,6 +98,10 @@ def get_pytest_env_vars() -> Dict[str, str]:
     "True",
     "true",
 )
+
+# Error if a python version is missing
+nox.options.error_on_missing_interpreters = True
+
 #
 # Style Checks
 #