Allow any_runners_available? callsite

This is responsible for 500 calls in our CI so will allow us to shrink
the spec based callsite

app/models/ci/build.rb

@@ -760,7 +760,9 @@ module Ci
 
     def any_runners_available?
       cache_for_available_runners do
-        project.active_runners.exists?
+        ::Gitlab::Database.allow_cross_joins_across_databases(url: 'https://gitlab.com/gitlab-org/gitlab/-/issues/339937') do
+          project.active_runners.exists?
+        end
       end
     end
 

app/models/project.rb

@@ -1784,6 +1784,9 @@ class Project < ApplicationRecord
     Ci::Runner.from_union([runners, group_runners, available_shared_runners])
   end
 
+  # Once issue 339937 is fixed, please search for all mentioned of
+  # https://gitlab.com/gitlab-org/gitlab/-/issues/339937,
+  # and remove the allow_cross_joins_across_databases.
   def active_runners
     strong_memoize(:active_runners) do
       all_available_runners.active

spec/support/database/cross-join-allowlist.yml

@@ -75,7 +75,6 @@
 - "./ee/spec/requests/api/vulnerability_findings_spec.rb"
 - "./ee/spec/serializers/dashboard_environment_entity_spec.rb"
 - "./ee/spec/serializers/dashboard_environments_serializer_spec.rb"
-- "./ee/spec/serializers/ee/build_details_entity_spec.rb"
 - "./ee/spec/serializers/merge_request_poll_widget_entity_spec.rb"
 - "./ee/spec/services/auto_merge/add_to_merge_train_when_pipeline_succeeds_service_spec.rb"
 - "./ee/spec/services/ci/create_pipeline_service/needs_spec.rb"
@@ -308,7 +307,6 @@
 - "./spec/requests/api/merge_requests_spec.rb"
 - "./spec/requests/api/package_files_spec.rb"
 - "./spec/requests/projects/cycle_analytics_events_spec.rb"
-- "./spec/serializers/build_details_entity_spec.rb"
 - "./spec/serializers/ci/pipeline_entity_spec.rb"
 - "./spec/serializers/merge_request_serializer_spec.rb"
 - "./spec/serializers/pipeline_details_entity_spec.rb"