internal: add phpunit tests #7

Job	Run time
phpunit-php-8-0 / PHPUnit tests (PHP 8.0)	46s
phpunit-php-8-1 / PHPUnit tests (PHP 8.1)	43s
phpunit-php-7-4 / PHPUnit tests (PHP 7.4)	49s
phpunit-php-8-2 / PHPUnit tests (PHP 8.2)	48s
phpunit-php-8-4 / PHPUnit tests (PHP 8.4)	1m 1s
phpunit-php-8-3 / PHPUnit tests (PHP 8.3)	40s
PHPUnit - Test Results Summary	3s
	4m 50s

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