MNT: explicitly cast np.bool_ -> bool to prevent deprecation warning

[tacaswell]

This is a workaround to https://bugs.python.org/issue37980

• np.bool raises a warning if you try to use it as an index (by
  warning in its __index__ method
• in py38 bpo-36048: Use __index__() instead of __int__() for implicit conversion if available. python/cpython#11952 python changes
  the code path used to convert np.bool_ -> int for as it is used in
  sorted so it now goes through the __index__ code path
• this causes a bunch of spurious warnings to come out of Matplotlib.

I see failures on this locally, but we do not see these failures on the azure pre-release, not sure why.

PR Summary

PR Checklist

• Has Pytest style unit tests
• Code is Flake 8 compliant

[tacaswell]

force-pushed to fix spelling 🙄

[tacaswell]

ok, I figured out why the python preview is not failing on azure, we are installing py3.8b4, but in the tests are falling back to py3.6.8.

[tacaswell]

This seems to be hitting https://bugs.python.org/issue37074 which looks like it has been fixed, but not an a tagged pre-release yet.

[tacaswell]

I just force-pushed a commit with in-line comments of why we are doing extra work, will open a PR later today with the "fix" to the azure pre-release python.

[tacaswell]

Although there is a chance that CPython will fix this before py3.8 is released, there is also a chance that they will decide that this is a NumPy problem so I think we should defensively merge this so we do not have to hold any release on a decision being made upstream (either in NumPy or Python).

[lumberbot-app]

Owee, I'm MrMeeseeks, Look at me.

There seem to be a conflict, please backport manually. Here are approximate instructions:

1. Checkout backport branch and update it.

$ git checkout v2.2.x
$ git pull

2. Cherry pick the first parent branch of the this PR on top of the older branch:

$ git cherry-pick -m1 b965c4d4603caac702fa2530ac88d35dd3bb4df9

3. You will likely have some merge/cherry-pick conflict here, fix them and commit:

$ git commit -am 'Backport PR #15168: MNT: explicitly cast np.bool_ -> bool to prevent deprecation warning'

4. Push to a named branch :

git push YOURFORK v2.2.x:auto-backport-of-pr-15168-on-v2.2.x

5. Create a PR against branch v2.2.x, I would have named this PR:

"Backport PR #15168 on branch v2.2.x"

And apply the correct labels and milestones.

Congratulation you did some good work ! Hopefully your backport PR will be tested by the continuous integration and merged soon!

If these instruction are inaccurate, feel free to suggest an improvement.

[tacaswell]

this code path is not in 2.2.x, these changes came in via 7f7b048 which is only in 3.1.1+

[QuLogic]

FTR, this works for Python 3.8.0b4: https://koji.fedoraproject.org/koji/taskinfo?taskID=37504715