Remove assertRegExp

[mitch292]

Resolves #4087

[codecov]

Codecov Report

Merging #4217 into master will not change coverage.
The diff coverage is n/a.

@@            Coverage Diff            @@
##             master    #4217   +/-   ##
=========================================
  Coverage     84.15%   84.15%           
  Complexity     4523     4523           
=========================================
  Files           219      219           
  Lines         11099    11099           
=========================================
  Hits           9340     9340           
  Misses         1759     1759           

Impacted Files	Coverage Δ	Complexity Δ
src/Framework/Assert.php	93.74% <ø> (ø)	223.00 <0.00> (ø)

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[sebastianbergmann]

Thank you for your contribution. I appreciate the time you invested in preparing this pull request. However, I have decided not to merge it as this has to wait until after the release of PHPUnit 9.5 and I do not want to have to keep this pull request in sync until then. In the future, please do not start to work on issues such as #4087 that have an assignee.