Add CI run that tests the package without numpy installed

[wshanks]

Given that it is common to work with Uncertainties and numpy, it is easy to forget to check that a hard dependency on numpy has been introduced. Here an extra run is added to the CI configuration to run the tests without installing numpy.

• Closes # (insert issue number)
• Executed pre-commit run --all-files with no errors
• The change is fully covered by automated unit tests
• Documented in docs/ as appropriate
• Added an entry to the CHANGES file

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 96.38%. Comparing base (9e0ba9a) to head (58f6817).

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #252      +/-   ##
==========================================
+ Coverage   95.80%   96.38%   +0.57%     
==========================================
  Files          15       15              
  Lines        1908     1909       +1     
==========================================
+ Hits         1828     1840      +12     
+ Misses         80       69      -11     

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[wshanks]

Oops, I had meant to open this against my fork first for iterating on the yaml syntax. It looks like it is good now.

At first, I experimented with adding a --skip-numpy option to pytest and marking all the numpy dependent tests so they would show up as skipped, but pytest tries to import all the test files as part of its collection so for this to work a lot of numpy related imports had to be put in try blocks. I didn't like how that would make numpy installation problems show up instead as "variable numpy is undefined" so I went with this simpler variant of just ignoring entirely the files that import numpy (and skipping on test in test_uncertainties that tries to import numpy).

[andrewgsavage]

nice this will be helpful!

[wshanks]

I think this one is simple enough to merge without more feedback (it doesn't affect the package itself).