Re-enable shared runners on descendants

What does this MR do and why?

Enabled shared runners on descendants

See more in Re-enable shared runners for sub-groups and pro... (#299823 - closed)

Previous refactoring: refactor: Move shared runners group logic to se... (!124164 - merged)

Screenshots or screen recordings

https://www.loom.com/share/485ab1fd11ae4e0da01b084842a81faf?sid=f3c60639-6421-4678-bd18-ff3ae6272527

How to set up and validate locally

See video above

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.