CloudFormation Specifications
- Update CloudFormation specs to `154.0.0` (pull [3005](https://github.com/aws-cloudformation/cfn-lint/pull/3005))
- Add db.serverless to neptune instance classes (pull [3009](https://github.com/aws-cloudformation/cfn-lint/pull/3009))
Fixes
- Drop python 3.7 support (pull [3005](https://github.com/aws-cloudformation/cfn-lint/pull/3005))