Make pytype respect required python versions of stubs

[hamdanal]

This is the pytype part of #10722

[AlexWaygood]

I just posted some explanation in #10722 (comment) of the context/history around why we pytype and pyright are run so differently from mypy in CI.

The result of all that is that pytype_test.py now only works if you've already done something like what we do in CI to install all the non-types dependencies for all our stubs packages:

typeshed/.github/workflows/tests.yml

Lines 71 to 80 in 3eb9ff7

	- run: pip install -r requirements-tests.txt
	- name: Install external dependencies for 3rd-party stubs
	run: |
	DEPENDENCIES=$(python tests/get_external_stub_requirements.py)
	if [ -n "$DEPENDENCIES" ]; then
	echo "Installing packages: $DEPENDENCIES"
	pip install $DEPENDENCIES
	fi
	- run: pip freeze --all
	- run: ./tests/pytype_test.py --print-stderr

(This probably isn't an ideal state of affairs; we should probably alter pytype_test.py so that it includes this logic and installs all these packages into a temporary venv, rather than having to run two scripts sequentially in order for the second one to work.)

As a result, I think this PR as it currently stands is insufficient, since tests/get_external_stub_requirements.py is probably still going to include matplotlib>=3.8 in its output after #10721 is merged, and matplotlib>=3.8 can't be installed with Python <3.9. (tests/get_external_stub_requirements.py already requires Python 3.9+ to even run, though; we require Python 3.9+ for all our tests except mypy_test.py, which needs to be compatible with Python 3.8.)

[hamdanal]

Thanks for the context. I’ll close this now.

[AlexWaygood]

No worries. Sorry I wasn't clearer earlier about the "philosophical difference" between this script and the mypy scripts :(

[hamdanal]

Don’t worry about it. I was happy it worked locally that I forgot to look how it works in CI. I will look into it again in the future when I get some time and if no one else beats me to it.