Resolve "Milestone sidebar display incorect number of MR when minimized"

What does this MR do?

Corrects the MR count in the milestone sidebar. It was counting memoized issues.

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

Why was this MR needed?

Screenshots (if relevant)

Does this MR meet the acceptance criteria?

• Changelog entry added, if necessary
• Documentation created/updated
• API support added
• Tests
  • Added for this feature/bug
  • All builds are passing
• Conform by the merge request performance guides
• Conform by the style guides
• Branch has no merge conflicts with master (if it does - rebase it please)
• Squashed related commits together

What are the relevant issue numbers?

Closes #31292 (closed)

added 2 commits

• aa364386 - Correct the resource counted for MR collapsed info
• 27317d55 - Added test

Compare with previous version

assigned to @filipa

This is more related to backend data structure than frontend

@smcgivern can you review this one please? Thanks!

assigned to @smcgivern

@lbennett thanks, can you add a changelog entry please?

assigned to @lbennett

added 1 commit

• 55fd112b - [ci skip] added changelog

Compare with previous version

@smcgivern Added changelog w/ ci skip, could you merge?

assigned to @smcgivern

approved this merge request

merged

mentioned in commit 976b020a

Picked into 9-1-stable, will go into 9.1.2

mentioned in commit 2d0e9173