Upgrade test tooling to PHPUnit 12 + add Infection/PHPStan + regression tests#1469

Refaltor77 wants to merge 2 commits into

discord-php:masterdiscord-php/DiscordPHP:masterfrom

Refaltor77:chore/test-tooling-and-unit-testsRefaltor77/DiscordPHP:chore/test-tooling-and-unit-testsCopy head branch name to clipboard