Fix : Hide issuable email address on sidebar with :moved_mr_sidebar on

What does this MR do and why?

Bugfix after !118763 (merged) merged to hide issuable email address with moved_mr_sidebar flag on as reported by @annabeldunstone in this comment

Screenshots or screen recordings

Before	After

How to set up and validate locally

Numbered steps to set up and validate the change are strongly suggested.

1. In rails console enable the flag

   Feature.enable(:moved_mr_sidebar)

2. Make sure your gdk is set up to use issuable email address - https://gitlab.com/gitlab-org/gitlab-development-kit/-/blob/main/doc/howto/service_desk_mail_room.md
3. Visit any issue/incident
4. Make sure that the issuable email address is not visible in the sidebar and only in the more actions dropdown
5. Now disable the FF
6. See that it is visible in the sidebar and not in the actions dropdown

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 #373757 (closed)