Update user cap banner link

What does this MR do and why?

It updates the link of the pending members' page inside the user cap banner link.

The banner is under saas_user_caps feature flag that's still under development.

Screenshots or screen recordings

There's no visual changes, here's the banner linking to the pending members (pending members page is still empty at the moment)

How to set up and validate locally

1. Enable saas_user_caps feature flag from rails console. (rails console then Feature.enable(:saas_user_caps))
2. With a group with an Ultimate plan
3. Navigate to Settings -> Permissions, LFS, 2FA -> User Cap
4. Set the user cap limit to 1
5. Navigate to the group members
6. Add one or more members (until you are above the user cap limit set in previous step)
7. Navigate to Settings
8. You should see an alert that you have pending members
9. Clicking the button in the alert should navigate to a pending members page

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 #344470 (closed)