[4.6] Replace importlib_metadata with importlib.metadata on Python 3.8+ (#5539)

[mimi1vx]

No description provided.

[nicoddemus]

Thanks again @mimi1vx,

Can you please rebase now that #5944 has been merged? Thanks!

[codecov]

Codecov Report

Merging #5945 into 4.6-maintenance will increase coverage by 0.27%.
The diff coverage is 71.42%.

@@                 Coverage Diff                 @@
##           4.6-maintenance    #5945      +/-   ##
===================================================
+ Coverage            95.92%   96.19%   +0.27%     
===================================================
  Files                  115      115              
  Lines                26560    26563       +3     
  Branches              2616     2617       +1     
===================================================
+ Hits                 25477    25552      +75     
+ Misses                 756      704      -52     
+ Partials               327      307      -20

Impacted Files	Coverage Δ
testing/test_assertion.py	97.67% <ø> (ø)	⬆️
src/_pytest/config/__init__.py	94.43% <100%> (ø)	⬆️
testing/acceptance_test.py	98.02% <100%> (+0.98%)	⬆️
testing/test_entry_points.py	100% <100%> (ø)	⬆️
testing/test_config.py	99.83% <100%> (+0.32%)	⬆️
src/_pytest/compat.py	95.14% <33.33%> (+2.04%)	⬆️
src/_pytest/fixtures.py	97.55% <0%> (+0.27%)	⬆️
testing/test_capture.py	99.25% <0%> (+0.29%)	⬆️
testing/test_terminal.py	99.84% <0%> (+0.31%)	⬆️
... and 17 more

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[nicoddemus]

Thanks again @mimi1vx!

Any other fixes you feel should be ported? Otherwise I plan to cut a new 4.6 release later today.