Tests

Bump requirements to currently supported Symfony versions, allow Symfony 8.x #139

Job	Run time
PHPUnit (PHP 8.1, Symfony version lock 6.4.*, prefer-lowest)	15s
PHPUnit (PHP 8.3, Symfony version lock 7.*, prefer-stable)	19s
PHPUnit (PHP 8.1, Symfony version lock 6.4.*, prefer-stable)	19s
PHPUnit (PHP 8.4, Symfony version lock 8.*, prefer-stable)	17s
	1m 10s

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