Run typechecking in CI again

[rnestler]

This enables type-checking during CI gain.

• Run mypy during CI #391 added typechcking during CI
• Modernize project setup #635 removed it again
• Enable mypy strict mode #429 is the long term target

Checklist:

• Add tests that demonstrate the correct behavior of the change. Tests should fail without the change.
• Add or update relevant docs, in the docs folder and in code.
• Add an entry in CHANGES.rst summarizing the change and linking to the issue.
• Add .. versionchanged:: entries in any relevant code docs.
• Run pre-commit hooks and fix any issues.
• Run pytest and tox, no tests failed.

[rnestler]

pyright currently shows quite some type checking errors. Since I don't have much experience with it I just removed it for now.

I think getting one type checker to run successfully in strict mode should be the first priority. Adding more afterwards can still be helpful.