Validate foreign key on ServiceHooks

In 13.7 we prevented invalid records
https://gitlab.com/gitlab-org/gitlab/-/merge_requests/47821 and fixed
existing records
https://gitlab.com/gitlab-org/gitlab/-/merge_requests/48263.

We can now validate the foreign key.

changelogs/unreleased/validate-foreign-key-service-hooks.yml

+---
+title: Validate foreign key on ServiceHooks
+merge_request: 57483
+author:
+type: other

db/migrate/20210325113129_validate_foreign_key_on_service_hooks.rb

+# frozen_string_literal: true
+
+class ValidateForeignKeyOnServiceHooks < ActiveRecord::Migration[6.0]
+  include Gitlab::Database::MigrationHelpers
+
+  DOWNTIME = false
+
+  CONSTRAINT_NAME = 'fk_d47999a98a'
+
+  def up
+    validate_foreign_key :web_hooks, :service_id, name: CONSTRAINT_NAME
+  end
+
+  def down
+    # no-op
+  end
+end

db/schema_migrations/20210325113129

+27fcdd54a21d554e44df621e409b81fe248e00851c856d315f4f64b463c7a5b7
\ No newline at end of file

db/structure.sql

@@ -25133,7 +25133,7 @@ ALTER TABLE ONLY ci_builds
     ADD CONSTRAINT fk_d3130c9a7f FOREIGN KEY (commit_id) REFERENCES ci_pipelines(id) ON DELETE CASCADE;
 
 ALTER TABLE ONLY web_hooks
-    ADD CONSTRAINT fk_d47999a98a FOREIGN KEY (service_id) REFERENCES services(id) ON DELETE CASCADE NOT VALID;
+    ADD CONSTRAINT fk_d47999a98a FOREIGN KEY (service_id) REFERENCES services(id) ON DELETE CASCADE;
 
 ALTER TABLE ONLY ci_sources_pipelines
     ADD CONSTRAINT fk_d4e29af7d7 FOREIGN KEY (source_pipeline_id) REFERENCES ci_pipelines(id) ON DELETE CASCADE;