refactor: remove phpunit CoversMethod

[didoda]

This removes phpunit CoversMethod from tests files.
It is not "repeatable", so it originated phpstan errors.
CoversClass is enough.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 98.6%. Comparing base (f4513c4) to head (67d6332).
⚠️ Report is 5 commits behind head on master.

Additional details and impacted files

@@           Coverage Diff            @@
##             master     #29   +/-   ##
========================================
  Coverage      98.6%   98.6%           
  Complexity       69      69           
========================================
  Files             7       7           
  Lines           227     227           
========================================
  Hits            224     224           
  Misses            3       3           

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