Add scheduled_at_before scope to CommitStatus

The query we use to get scheduled builds in this service has been
thoroughly reviewed and optimized. We should make the query available
to other parts of the application.

app/models/commit_status.rb

@@ -62,6 +62,9 @@ class CommitStatus < Ci::ApplicationRecord
   scope :updated_before, ->(lookback:, timeout:) {
     where('(ci_builds.created_at BETWEEN ? AND ?) AND (ci_builds.updated_at BETWEEN ? AND ?)', lookback, timeout, lookback, timeout)
   }
+  scope :scheduled_at_before, ->(date) {
+    where('ci_builds.scheduled_at IS NOT NULL AND ci_builds.scheduled_at < ?', date)
+  }
 
   # The scope applies `pluck` to split the queries. Use with care.
   scope :for_project_paths, -> (paths) do

app/services/ci/stuck_builds/drop_scheduled_service.rb

@@ -16,10 +16,7 @@ module Ci
       private
 
       def scheduled_timed_out_builds
-        Ci::Build.where(status: :scheduled).where( # rubocop: disable CodeReuse/ActiveRecord
-          'ci_builds.scheduled_at IS NOT NULL AND ci_builds.scheduled_at < ?',
-          BUILD_SCHEDULED_OUTDATED_TIMEOUT.ago
-        )
+        Ci::Build.scheduled.scheduled_at_before(BUILD_SCHEDULED_OUTDATED_TIMEOUT.ago)
       end
     end
   end

spec/models/commit_status_spec.rb

@@ -123,6 +123,16 @@ RSpec.describe CommitStatus do
     end
   end
 
+  describe '.scheduled_at_before' do
+    let!(:never_scheduled) { create(:commit_status) }
+    let!(:stale_scheduled) { create(:commit_status, scheduled_at: 1.day.ago) }
+    let!(:fresh_scheduled) { create(:commit_status, scheduled_at: 1.minute.ago) }
+
+    subject { CommitStatus.scheduled_at_before(1.hour.ago) }
+
+    it { is_expected.to contain_exactly(stale_scheduled) }
+  end
+
   describe '#processed' do
     subject { commit_status.processed }