Fix mutation tests

[vjik]

Q	A
Is bugfix?	❌
New feature?	❌
Breaks BC?	❌

[what-the-diff]

PR Summary

• Update PHP Version
  The PHP version used in our automated testing process (specifically in mutation.yml) has been upgraded from version 8.1/8.2 to the newer version 8.3. This ensures our code is compatible with the latest PHP updates.

• Modification of run Command
  The command used to execute our 'Infection' test (a type of test for checking code quality applied in the Run infection step) has been updated. The instruction now includes --threads=2 flag, meaning the test will split its workload into two parts and run them concurrently. This can potentially improve the speed of our testing process.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (ed3537e) 100.00% compared to head (3e5f754) 100.00%.

Additional details and impacted files

@@             Coverage Diff             @@
##              master       #60   +/-   ##
===========================================
  Coverage     100.00%   100.00%           
  Complexity        16        16           
===========================================
  Files              2         2           
  Lines             96        96           
===========================================
  Hits              96        96           

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