Add `#[CoversNothing]` to classes which test other test-artifacts #22883

Job	Run time
Compiler Tests	1m 43s
extension-tests / Check PHAR checksum	6s
integration-tests / Check PHAR checksum	7s
other-tests / Check PHAR checksum	7s
Download base SHA PHAR	0s
PHAR Prefix Diff	0s
Checksum PHAR	0s
Commit PHAR	0s
extension-tests / ${{ matrix.extension-name }} (${{ matrix.php-version }}) ${{ matrix.script }}	0s
integration-tests / Integration - ${{ matrix.repo }}	0s
integration-tests / Integration - ${{ matrix.name }}	0s
integration-tests / PMMP Tests	0s
integration-tests / Integration - Update baselines	0s
other-tests / Other Tests	-1s
	2m 2s

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