Add hooks to check backwards compatibility with py3.6+

[AlpAribal]

Description

Updates flake8 hook version and introduces two flake8-plugins to check for backwards-incompatible syntax.

• flake8-walrus check for the usage of the walrus operator and warns if used
• flake8-typing-imports checks for incompatible imports of the typing module

Type of change

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Documentation update
• Refactoring including code style reformatting
• Other (please describe):

Checklist:

• I have read the contributing guideline doc (external contributors only)
• Lint and unit tests pass locally with my changes
• I have kept the PR small so that it can be easily reviewed
• I have made corresponding changes to the documentation
• I have added tests that prove my fix is effective or that my feature works
• All dependency changes have been reflected in the pip requirement files.

[AlirezaSohofi]

LG 👍