Skip Backfill groups in the periodic pipeline (#195760)

## Summary

This test shouldn't run in periodic pipeline. We expect only FTR and Cypress running in periodic and 2nd quality gate pipelines enabled in #193666.

(cherry picked from commit 6f1449b)

x-pack/test/security_solution_cypress/cypress/e2e/detection_response/rule_management/rule_details/backfill_group.cy.ts

@@ -34,7 +34,7 @@ import {
 describe(
   'Backfill groups',
   {
-    tags: ['@ess', '@serverless'],
+    tags: ['@ess', '@serverless', '@skipInServerlessMKI'],
   },
   function () {
     before(() => {