fix(coverage): Add no cover pragma for api_key import

Author: chalmerlowe

google/cloud/client/__init__.py

@@ -34,8 +34,9 @@
     import google.auth.api_key
 
     HAS_GOOGLE_AUTH_API_KEY = True
-except ImportError:
-    HAS_GOOGLE_AUTH_API_KEY = False
+except ImportError:  # pragma: no cover
+    HAS_GOOGLE_AUTH_API_KEY = False  # pragma: no cover
+    # TODO: Investigate adding a test for google.auth.api_key ImportError (https://github.com/googleapis/python-cloud-core/issues/334)
 
 
 _GOOGLE_AUTH_CREDENTIALS_HELP = (