added github token to solve composer rate limit

[AlessandroMinoccheri]

This PR should fix: #353

I found the possible solution here:
shivammathur/setup-php#679

Unfortunately, secrets can't start with the word GITHUB

[codecov-commenter]

Codecov Report

Merging #354 (772a74e) into main (5667de6) will increase coverage by 0.03%.
The diff coverage is 96.15%.

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@@             Coverage Diff              @@
##               main     #354      +/-   ##
============================================
+ Coverage     93.80%   93.83%   +0.03%     
- Complexity      492      495       +3     
============================================
  Files            60       60              
  Lines          1323     1330       +7     
============================================
+ Hits           1241     1248       +7     
  Misses           82       82              

Impacted Files	Coverage Δ
src/Analyzer/FullyQualifiedClassName.php	96.55% <83.33%> (-3.45%)	⬇️
src/Analyzer/ClassDescription.php	100.00% <100.00%> (ø)
src/Analyzer/ClassDescriptionBuilder.php	100.00% <100.00%> (ø)
src/Analyzer/FileVisitor.php	82.40% <100.00%> (ø)
src/Expression/ForClasses/Extend.php	100.00% <100.00%> (+8.33%)	⬆️

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