Pin mypy version

[Czaki]

Description

This PR pin mypy version is used for test typing and enabling dependaboot to create PR with updates of mypy related things.

This will allow us to not get unrelated failures in PR.

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)
• This change requires a documentation update

References

How has this been tested?

• example: the test suite for my feature covers cases x, y, and z
• example: all tests pass with my change
• example: I check if my changes works with both PySide and PyQt backends
  as there are small differences between the two Qt bindings.

Final checklist:

• My PR is the minimum possible work for the desired functionality
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• I have added tests that prove my fix is effective or that my feature works
• If I included new strings, I have used trans. to make them localizable.
  For more information see our translations guide.

[kephale]

Awesome, @Czaki!

[Czaki]

I see benefits from pin mypy but I'm not sure if two others also should be pinned. On one side it reduces the probability of random error, on the other side, I do not remember errors with this packages. Maybe release this versions to reduce dependaboot PRs?

[kephale]

I agree and vote to pin them. There is a strong advantage to having consistent type checking, so it is nice to make sure these packages don't change unexpectedly.

[brisvag]

Yeah I agree, I don't mind a few extra PRs if it means we don't get spurious unexpected failures.