Markdown editor: FIx alignment of notification warning

What does this MR do and why?

Markdown editor: FIx alignment of notification warning.

Screenshots or screen recordings

Before	After

How to set up and validate locally

1. Go to an issue (e.g. http://gdk.test:3000/flightjs/Flight/-/issues/3)
2. Type @all in the Markdown editor
3. Check warning

MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• I have evaluated the MR acceptance checklist for this MR.

Related to #408231 (closed)