#43691: DiffNotes not counted by ContributionsCalendar

Fix #43691 (closed)

Query plan before this change: https://explain.depesz.com/s/V7O

Query plan after this change: https://explain.depesz.com/s/b8LL

Does this MR meet the acceptance criteria?

• Changelog entry added, if necessary
• Documentation created/updated
• API support added
• Tests added for this feature/bug
• Review
  • Has been reviewed by UX
  • Has been reviewed by Frontend
  • Has been reviewed by Backend
  • Has been reviewed by Database
• Conform by the merge request performance guides
• Conform by the style guides
• Squashed related commits together
• Internationalization required/considered
• End-to-end tests pass (package-qa manual pipeline job)

What are the relevant issue numbers?