Reduce overhead of LabelFinder by avoiding #presence call

Some users experienced 502 timeouts when viewing group labels.
Labels#open_issues_count and Label#open_merge_requests_count were
taking a long time to load because they were loading every ActiveRecord
of the user-accessible projects into memory. This change modifies the system
so that #presence and hence to_a isn't called.

Closes #23684

CHANGELOG.md

@@ -20,6 +20,7 @@ Please view this file on the master branch, on stable branches it's out of date.
   - Fix reply-by-email not working due to queue name mismatch
   - Fixed hidden pipeline graph on commit and MR page !6895
   - Expire and build repository cache after project import
+  - Reduce overhead of LabelFinder by avoiding #presence call !7094
   - Fix 404 for group pages when GitLab setup uses relative url
   - Simpler arguments passed to named_route on toggle_award_url helper method 
   - Better handle when no users were selected for adding to group or project. (Linus Thiel)

app/finders/labels_finder.rb

@@ -48,7 +48,7 @@ class LabelsFinder < UnionFinder
   end
 
   def projects_ids
-    params[:project_ids].presence
+    params[:project_ids]
   end
 
   def title