Tests

Fix `MixedType->equals(ErrorType)` #21487

Job	Run time
Determine levels tests matrix	28s
Integration tests (ubuntu-latest)	40s
Tests with old PHPUnit (7.4, ubuntu-latest)	6m 4s
Tests with old PHPUnit (8.0, ubuntu-latest)	1m 54s
Tests with old PHPUnit (7.4, windows-latest)	13m 19s
Tests with old PHPUnit (8.1, windows-latest)	3m 28s
Tests (8.3, ubuntu-latest)	37s
Integration tests (windows-latest)	1m 34s
Tests with old PHPUnit (8.1, ubuntu-latest)	1m 51s
Tests with old PHPUnit (8.0, windows-latest)	3m 22s
Tests (8.3, windows-latest)	1m 30s
Tests (8.2, ubuntu-latest)	42s
Tests (8.2, windows-latest)	1m 36s
Tests (8.4, windows-latest)	1m 31s
Tests (8.4, ubuntu-latest)	37s
Levels tests	0s
	39m 13s

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