Enhancement: Update phpunit/phpunit

[localheinz]

This pull request

• updates phpunit/phpunit

[codecov]

Codecov Report

Merging #346 (c02cc13) into main (6c774db) will increase coverage by 0.22%.
The diff coverage is n/a.

@@             Coverage Diff              @@
##               main     #346      +/-   ##
============================================
+ Coverage     93.18%   93.40%   +0.22%     
  Complexity       88       88              
============================================
  Files            11       11              
  Lines           176      182       +6     
============================================
+ Hits            164      170       +6     
  Misses           12       12              

Impacted Files	Coverage Δ
src/FakeVariables.php	100.00% <0.00%> (ø)
src/ReadOnlyVariables.php	100.00% <0.00%> (ø)

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