"slick_requirements without a #[LegacyRequirementsHook] attribute is deprecated in drupal:11.3.0 and removed in drupal:13.0.0." [#3618587]

Problem/Motivation

Running tests of a custom module on D11.4, I get this:
slick_requirements without a #[LegacyRequirementsHook] attribute is deprecated in drupal:11.3.0 and removed in drupal:13.0.0. See https://www.drupal.org/node/3549685

Steps to reproduce

Run tests of a module on D11.4/PHP 8.3 or similar.

Proposed resolution

I'll create an MR.

Remaining tasks

Test BC.

Issue fork slick-3618587

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3618587-slickrequirements-without-a changes, plain diff MR !22
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