[stable29] fix(files): ensure forbiddenCharacters is an array

[Antreesy]

• Resolves: regression from [stable29] fix(files): validate input when creating file/directory #46718
• Something tells me we should test before merging

Before	After
\/:; string	(4) ['\\', '/', ':', ';'] 'object'

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)

[Antreesy]

/compile

[Antreesy]

/backport 7ea8ace to stable28