test: files_sharing add test for LoadAdditionalListener

[printminion-co]

Summary

Adds test for apps/files_sharing/lib/Listener/LoadAdditionalListener.php in order to be able to additional functionality later

Test via:

phpunit --bootstrap tests/bootstrap.php apps/files_sharing/tests/Listener/LoadAdditionalListenerTest.php

Checklist

• Code is properly formatted
• Sign-off message is added to all commits
• Tests (unit, integration, api and/or acceptance) are included
• Screenshots before/after for front-end changes
• Documentation (manuals or wiki) has been updated or is not required
• Backports requested where applicable (ex: critical bugfixes)

[github-actions]

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[printminion-co]

/backport to stable30

[printminion-co]

/backport to stable31

[skjnldsv]

Thanks @printminion-co !!