Fix unregistration logic for pull diagnostics (#44294)

Even if `workspace_diagnostics_refresh_tasks` is empty, registrations
which didn't advertise support for workspace diagnostics may still
exist.

Release Notes:

- N/A
9e33243015John Tur committed on 12/6/2025, 4:31:05 PM· committed by GitHubparenta0848da
1 file changedLine totals unavailable