Advanced Search: fix project count_only queries

ee/changelogs/unreleased/321620-fix-project-count-only-queries.yml

+---
+title: 'Advanced Search: fix project count_only queries'
+merge_request: 54303
+author:
+type: fixed

ee/lib/elastic/latest/project_class_proxy.rb

@@ -44,7 +44,7 @@ module Elastic
             }
           end
 
-          query_hash[:query][:bool][:filter] = filters
+          query_hash[:query][:bool][:filter] += filters
         end
 
         search(query_hash, options)

ee/spec/lib/gitlab/elastic/search_results_spec.rb

@@ -1269,6 +1269,16 @@ RSpec.describe Gitlab::Elastic::SearchResults, :elastic, :sidekiq_might_not_need
         expect(projects).to include public_project
         expect(results.projects_count).to eq 1
       end
+
+      it 'returns 0 results for count only query' do
+        public_project
+
+        ensure_elasticsearch_index!
+
+        results = described_class.new(user, 'noresults')
+        count = results.formatted_count('projects')
+        expect(count).to eq('0')
+      end
     end
 
     context 'merge requests' do