[Docs] Fix typo in skipping.rst

[dougthor42]

One of the pytest.mark.skipif blocks in docs/skipping.rst does not use the reason kwarg:

pytestmark = pytest.mark.skipif(sys.platform == "win32", "tests for linux only")

This causes an error during setup of test:

Failed: you need to specify reason=STRING when using booleans as conditions.

This PR fixes the typo by adding reason=.

-pytestmark = pytest.mark.skipif(sys.platform == "win32", "tests for linux only")
+pytestmark = pytest.mark.skipif(sys.platform == "win32", reason="tests for linux only")

Note: I did not make an associated Issue or Changelog entry for this PR because of how trivial it is. If that's needed, please let me know.

[codecov]

Codecov Report

Merging #5135 into master will increase coverage by <.01%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master    #5135      +/-   ##
==========================================
+ Coverage   96.05%   96.06%   +<.01%     
==========================================
  Files         114      114              
  Lines       25784    25784              
  Branches     2550     2550              
==========================================
+ Hits        24768    24770       +2     
+ Misses        705      704       -1     
+ Partials      311      310       -1

Impacted Files	Coverage Δ
testing/acceptance_test.py	98.03% <0%> (+0.39%)	⬆️

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