Resolve "Count query for issues and MRs runs twice on group index"

What does this MR do?

Fix two double COUNT queries running on group pages.

Are there points in the code the reviewer needs to double check?

Don't think so!

Why was this MR needed?

It's a silly bug. There's not much performance impact though.

Does this MR meet the acceptance criteria?

• Changelog entry added, if necessary
• Review
  • Has been reviewed by Backend
• Conform by the merge request performance guides
• Conform by the style guides

What are the relevant issue numbers?

Closes #41546 (closed).