Add support for PHP 8

[villfa]

Closes #229

[codecov]

Codecov Report

Merging #256 (461a3e6) into master (5d9498b) will decrease coverage by 0.00%.
The diff coverage is n/a.

@@             Coverage Diff              @@
##             master     #256      +/-   ##
============================================
- Coverage     96.15%   96.14%   -0.01%     
  Complexity      176      176              
============================================
  Files            24       24              
  Lines           442      441       -1     
============================================
- Hits            425      424       -1     
  Misses           17       17              

Impacted Files	Coverage Δ	Complexity Δ
src/Result/HighestScores.php	100.00% <ø> (ø)	11.00 <0.00> (ø)

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[villfa]

The build fails because of a problem with phpunit-bridge. See symfony/symfony#38921