Mypy integration

[Domejko]

Description

• Created mypy CI workflow and updated README.md and docs/contributing/ setup.md accordingly.
• Added mypy pre-commit hook.
• Removed redundant matrix from run_djlint.yml.
• Updated github actions/* to latest versions.

Checklist

• Ran the Black Formatter and
  djLint-er on any new code
  (checks
  will
  fail without)
• Made any changes or additions to the documentation where required
• Changes generate no new warnings/errors
• New and existing unit tests pass locally with my
  changes

What type of PR is this?

• ✨ Feature
• 📝 Documentation Update

Added/updated tests?

• 🙅 no, because they aren't needed

Related PRs, Issues etc

• Related Issue #
• Closes #

[TreyWW]

Amazing PR, thank you @Domejko!