Add custom marker for checking validation (boto#3209)

Co-authored-by: Alessandra Romero <lromales@amazon.com>

tests/functional/test_h2_required.py

@@ -50,13 +50,15 @@ def _all_test_cases():
 H2_SERVICES, H2_OPERATIONS = _all_test_cases()
 
 
+@pytest.mark.validates_models
 @pytest.mark.parametrize("h2_service", H2_SERVICES)
 def test_all_uses_of_h2_are_known(h2_service):
     # Validates that a service that requires HTTP 2 for all operations is known
     message = 'Found unknown HTTP 2 service: %s' % h2_service
     assert _KNOWN_SERVICES.get(h2_service) is _H2_REQUIRED, message
 
 
+@pytest.mark.validates_models
 @pytest.mark.parametrize("h2_service, operation", H2_OPERATIONS)
 def test_all_h2_operations_are_known(h2_service, operation):
     # Validates that an operation that requires HTTP 2 is known