Update Project Policy Pending Membership Specs

What does this MR do and why?

Update the project policy pending membership specs to test each role rather than just the developer role.

Follow up from !80679 (comment 844036015).

Issue: #332598 (closed)

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.