Exclude stack policy when running in check mode. (#31940)

Fixes #31931

lib/ansible/modules/cloud/amazon/cloudformation.py

@@ -539,7 +539,8 @@ def main():
     else:
         stack_params['NotificationARNs'] = []
 
-    if module.params['stack_policy'] is not None:
+    # can't check the policy when verifying.
+    if module.params['stack_policy'] is not None and not module.check_mode:
         stack_params['StackPolicyBody'] = open(module.params['stack_policy'], 'r').read()