MWAA verify_env script incorrectly fails on checking public access block

[daniel-bowman-nationwide]

aws-support-tools/MWAA/verify_env/verify_env.py

Line 755 in 2a9b970

raise

It should be fine to error on either bucket level or account level block. This raise causes script to break if permissions prevent checking public access block but permissions are available for account level block. Changing to return None worked as a temporary fix.