[4.6] chore: add PHP 8.4 to test-phpunit.yml

[kenjis]

Description Supersedes #9133 See #9116

• add PHP 8.4 to test-phpunit.yml
• add --ignore-platform-req=php temporarily to @composer update --working-dir=utils

Checklist:

• [x] Securely signed commits
• [ ] Component(s) with PHPDoc blocks, only if necessary or adds value
• [ ] Unit testing, with >80% coverage
• [ ] User guide updated
• [ ] Conforms to style guide