Resolve "Improve the wording of Anyone can register notification"

What does this MR do and why?

This MR was created to resolve this issue.

It updates the copy in the alert that warns admins that sign up is enabled on their GitLab instance.

Screenshots or screen recordings

Before	After

How to set up and validate locally

1. Sign in as an admin
2. Navigate to /admin/application_settings/general. In the Sign-up restrictions panel check the Sign-up enabled checkbox.
3. Clear closed callouts
   • bin/rails console
   • Users::Callout.where({ feature_name: 25 }).destroy_all

MR acceptance checklist

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