[MAINT] various test updates

[ogrisel]

Trying to use the latest versions of pytest and coverage and attempting to avoid a random failure of test_child_raises_parent_exits_cleanly on macos CI.

[codecov]

Codecov Report

Base: 93.81% // Head: 93.81% // No change to project coverage 👍

Coverage data is based on head (4a314b1) compared to base (4a314b1).
Patch has no changes to coverable lines.

❗ Current head 4a314b1 differs from pull request most recent head 80edf6b. Consider uploading reports for the commit 80edf6b to get more accurate results

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #1334   +/-   ##
=======================================
  Coverage   93.81%   93.81%           
=======================================
  Files          52       52           
  Lines        7303     7303           
=======================================
  Hits         6851     6851           
  Misses        452      452           

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