Tests: don't mark PHP 8.1 & 8.2 tests as experimental

[spacedmonkey]

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• This is a non-user-facing change and requires no QA

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• This PR addresses an existing issue and I have linked this PR to it in ZenHub
• I have tested this code to the best of my abilities
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• This code is covered by automated tests (unit, integration, and/or e2e) to verify it works as intended (docs)
• I have added documentation where necessary
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Fixes #