Tests

Introduce all-methods-are-(im)pure #23128

Job	Run time
Integration tests (ubuntu-latest)	32s
Integration tests (windows-latest)	1m 38s
Determine levels tests matrix	34s
Tests with old PHPUnit (8.0, ubuntu-latest)	2m 6s
Tests (8.2, windows-latest)	1m 34s
Tests with old PHPUnit (7.4, windows-latest)	3m 32s
Tests with old PHPUnit (8.1, ubuntu-latest)	2m 10s
Tests with old PHPUnit (8.0, windows-latest)	3m 33s
Tests (8.2, ubuntu-latest)	32s
Tests with old PHPUnit (7.4, ubuntu-latest)	2m 12s
Tests (8.3, ubuntu-latest)	31s
Tests with old PHPUnit (8.1, windows-latest)	3m 38s
Tests (8.4, windows-latest)	1m 34s
Tests (8.3, windows-latest)	1m 32s
Tests (8.5, ubuntu-latest)	33s
Tests (8.4, ubuntu-latest)	31s
Tests (8.5, windows-latest)	1m 44s
Levels tests	0s
	28m 26s

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