[MA-21]: Added role='alert' to the error message element

[ayush-chauhan233]

Summary

• Added role='alert' to the error message element

Steps to reproduce

• Locate the "Unable to update the channel member." in the notification preference button inside the view info button in the channel header form field with an inline error.
• Inspect its element with Chrome DevTools.
• In the Accessibility tab, expand the Computed Properties section.

Review the value for "Description".

Expected Behavior

• The screen reader should announce the selected to keyboard interacted suggested item correctly.

Ticket Link

Jira https://mattermost.atlassian.net/browse/MM-61645

Screenshots

Release Note

NONE