Fix issues analytics query

When issues were being ordered by priority the issues analyitics query
was breaking. This commit ignores the order in the query.

ee/app/models/issuables_analytics.rb

@@ -34,6 +34,7 @@ class IssuablesAnalytics
   def issues_created_at_dates
     strong_memoize(:issues_created_at_dates) do
       issuables
+        .reorder(nil)
         .where('issues.created_at >= ?', months_back.months.ago.beginning_of_month)
         .pluck('issues.created_at')
         .map { |date| date.strftime(DATE_FORMAT) }

ee/changelogs/unreleased/issue_8475.yml

+---
+title: Fix issues analytics query when ordering issues by priority
+merge_request: 8509
+author:
+type: fixed

ee/spec/models/issuables_analytics_spec.rb

@@ -20,6 +20,18 @@ describe IssuablesAnalytics do
       end
     end
 
+    context 'when issuable relation is ordered by priority' do
+      it 'generates chart data correctly' do
+        issues = project.issues.order_by_position_and_priority
+        data = described_class.new(issuables: issues).data
+
+        seed.each_pair do |months_back, issues_count|
+          date = months_back.months.ago.strftime(described_class::DATE_FORMAT)
+          expect(data[date]).to eq(issues_count)
+        end
+      end
+    end
+
     context 'when months_back parameter is nil' do
       it 'returns a hash containing the issues count created in the past 12 months' do
         data = described_class.new(issuables: project.issues).data