[Security Solution] Unskip urls/not_found Serverless Cypress tests (#…

…169243)

**Addresses:** #161540

## Summary

This PR unskips `urls/not_found.cy.ts` Serverless Cypress tests.

## Flaky test runner

`urls/not_found.cy.ts` [150 runs](https://buildkite.com/elastic/kibana-flaky-test-suite-runner/builds/3590)

x-pack/test/security_solution_cypress/cypress/e2e/urls/not_found.cy.ts

@@ -25,8 +25,7 @@ import { editRuleUrl } from '../../urls/edit_rule';
 
 const mockRuleId = '5a4a0460-d822-11eb-8962-bfd4aff0a9b3';
 
-// FLAKY: https://github.com/elastic/kibana/issues/165710
-describe('Display not found page', { tags: ['@ess', '@serverless', '@brokenInServerless'] }, () => {
+describe('Display not found page', { tags: ['@ess', '@serverless'] }, () => {
   beforeEach(() => {
     login();
     visitWithTimeRange(TIMELINES_URL);