Use keyword-only arguments in a few places

[nicoddemus]

No description provided.

[asottile]

dope

[codecov]

Codecov Report

Merging #5398 into master will decrease coverage by 1.55%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master    #5398      +/-   ##
==========================================
- Coverage    94.5%   92.95%   -1.55%     
==========================================
  Files         114      114              
  Lines       25508    25673     +165     
  Branches     2480     2495      +15     
==========================================
- Hits        24106    23864     -242     
- Misses       1091     1484     +393     
- Partials      311      325      +14

Impacted Files	Coverage Δ
src/_pytest/pytester.py	90.58% <100%> (-0.01%)	⬇️
src/_pytest/outcomes.py	95.58% <100%> (-0.19%)	⬇️
testing/logging/test_reporting.py	20.76% <0%> (-79.24%)	⬇️
testing/examples/test_issue519.py	33.33% <0%> (-66.67%)	⬇️
testing/test_warnings.py	46.34% <0%> (-53.66%)	⬇️
testing/test_unittest.py	70.37% <0%> (-28.7%)	⬇️
src/_pytest/unittest.py	81.27% <0%> (-13.64%)	⬇️
testing/python/metafunc.py	84.83% <0%> (-9.55%)	⬇️
src/_pytest/logging.py	86.49% <0%> (-9.33%)	⬇️
testing/python/collect.py	92.35% <0%> (-7.01%)	⬇️
... and 15 more

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