Remove MockAwareDoctestFinder
I think the MockAwareDoctestFinder code from https://github.com/thisch/pytest-sphinx/blob/0e4ec60b720ba8d6afd1cf24e2a20e3ba8d6dd4f/pytest_sphinx.py#L494 can be removed (once we drop support for < python 3.10), because the issue we had with it has been fixed (I guess)
https://bugs.python.org/issue35753
Once we have python3.10 in the CI, we can try to check if this code is no longer needed.
If we removed MockAwareDoctestFinder we will be able to remove warn_unused_ignores = true (ef5cdfae69c41bcc3c89addcf6229a68bb9d627b)
The python version condition + type:ignore causes issues when running against CI with python versions matrix'd (see: https://github.com/python/mypy/issues/8823)