Update file scim_setup.md

What does this MR do and why?

Now that GitLab will delete unverified users after 1 day. We want to make sure that this change is also called out in SCIM provisioning. I recently had a customer who followed the SCIM documents but wasn't aware of the domain verification changes and they had to re-provision users several times due to the auto-deletion.

Screenshots or screen recordings

Screenshots are required for UI changes, and strongly recommended for all other merge requests.

Before	After

How to set up and validate locally

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

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.