Travis CI: install typing on python2 to restore some skipped tests

[vbarbaresi]

Description

Fixes #9473

Typing used to be installed on python2 but was removed by this change, I don't know why

in mypy/util.py:try_find_python2_interpreter() we try to find a valid python2 interpreter with typing installed.
If we don't find it, those tests are skipped.

However on typeshed, the CI installs typing on python2 for mypy self test. Thus it doesn't skip the tests.

This caused the regression issue on typeshed

Test Plan

I ran Travis CI on my forked repo.
I based a branch on 3186281 (the one that caused a python2 regression) and was able to reproduce the failing test: https://travis-ci.org/github/vbarbaresi/mypy/jobs/732473410
I noted that this change unskips around 40 tests (all from testpythoneval.py)

[vbarbaresi]

I just read in testpythoneval.py:

Note: These test cases are not included in the main test suite, as including
this suite would slow down the main suite too much.

So it looks like this was removed on purpose. Closing.

[hauntsaninja]

Thanks for looking into this and fixing!
I think it might actually have been unintentional, eg since we do run the other pythoneval tests in CI / it's not called out in the PR you linked. I think the comment might be referring to the fact that the evaluation tests are separated out here:

mypy/runtests.py

Line 22 in 3e77959

EVALUATION = 'PythonEvaluation'

(edit: just git blamed, and that comment is from 2014, four years apart from the "CI upgrades" PR...)

I'm going to reopen this, and maybe someone else who knows for sure can chime in :-)

[JukkaL]

The removal of Python 2 typing seems accidental. It would be nice to run the tests in CI.

[hauntsaninja]

Great! Thanks again, vbarbaresi