Service Desk: Move full stop out of Learn more link

What does this MR do and why?

Move full stop out of Learn more link inside Service Desk settings

MR acceptance checklist

✅ MR acceptance checklist.

Screenshots or screen recordings

How to set up and validate locally

1. Checkout this branch locally and start GDK
2. Open a test project and go to Settings -> General
3. Click on Expand inside the Service Desk section. You might not see any content if Service Desk is not enabled for the project. As a workaround, open app/views/projects/_service_desk_settings.html.haml and replace ::Gitlab::ServiceDesk.supported? with true. This will force the Service Desk content to render. (You might need to gdk restart to see the changes)
4. Click the Activate Service Desk button.
5. Locate the text To add a custom suffix, set up a Service Desk email address. Learn more. and verify that the full stop at the end is not part of the link
6. To see the alternative text we need to make sure Service Desk email is enabled. Go back to app/views/projects/_service_desk_settings.html.haml and replace Gitlab::Email::ServiceDeskEmail.enabled? with true. This will force the alternative content to render.
7. Locate the text Add a suffix to Service Desk email address. Learn more . and verify the full stop at the end is not part of the link

GL

Related to #414681