Github actions mypy build check fails when python 3.9 typing is used

[jacobcook1995]

Describe the bug
When the inbuilt type notation introduced in python 3.9 (e.g. list[str]) is used, the pre-commit/action@v2.0.2 fails the mypy build check. This is despite it passing the pre-commit hook locally.

To Reproduce
Steps to reproduce the behavior:

1. Add a type hint which indexes a collection type (e.g. list[str] or tuple[int]) to existing code
2. Commit this code
3. If it passes the pre-commit hooks push the code
4. The GitHub actions build check should fail with a message similar to error: "list" is not subscriptable, use "typing.List" instead

Expected behavior
The mypy build check should pass as we have set our supported python to be >=3.9.

Desktop (please complete the following information):

• OS: macOS
• Version 12.5.1

[davidorme]

I think we just need to add a python-version section to the qa job

[davidorme]

Yeah - the ubuntu-latest is Ubuntu 20.04, which includes Python 3.8, so that is what is being used:

https://wiki.ubuntu.com/FocalFossa/ReleaseNotes#:~:text=In%2020.04%20LTS%2C%20the%20python,base%20system%20is%20Python%203.8.

[davidorme]

OK, so I think we'll just need to add an extra step:

    - uses: actions/setup-python@v4
      with:
        python-version: "3.9"

I think it makes sense to just use the lowest version we want to support.