Fix atwho keypress cancel Issue

What does this MR do and why?

This MR is meant to solve this Issue: #362122 (comment 976131577) which is a part of the Beautifying our UI Initiative.

It fixes a bug, that when answering to a comment (on an Issue or a MR) and the User would try to leave at who menu (typing : or @ for example) by hitting the esc key. A Modal would appear asking if the user would want to cancel writing the comment. This is no longer the case: when the atwho menu is active the modal will not appear.

Screenshots or screen recordings

before	after
esc-before	esc-after

How to set up and validate locally

1. Go to any Merge Request or Issue
2. Find a comment on them
3. Create a reply for the comment
4. Open the atwho menu by typing :100 or @
5. hit the esc key
6. see no modal 🙂

MR acceptance checklist

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