Remove aria-hidden attribute from FormFieldMsg

[deleonio]

Refs: #6660

The A11y and PO reviews will only take place after all other DoD steps have been completed by the Developer:

• Meaningful pull request title for the release notes
• Pull request is linked to an issue and all changes relate to the issue
• Tests to protect this code implemented (if applicable)
• Manual test performed successfully (if applicable)
• Documentation or migration has been updated (if applicable)

[github-actions]

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