[Security Solution][Endpoint] Fix and unskip flaky test (elastic#165466)

## Summary

Fixes and un-skips a test. Ensures that the test data doesn't create an
existing index. If it still does, as a temp. measure we're dismissing
the error toast that is blocking the button so the rest of the test can
continue.

closes elastic/issues/139260

**flakey test runner**

https://buildkite.com/elastic/kibana-flaky-test-suite-runner/builds/3036
x 200 ( all green)

### Checklist

- [x] [Unit or functional
tests](https://www.elastic.co/guide/en/kibana/master/development-tests.html)
were updated or added to match the most common scenarios

x-pack/plugins/security_solution/common/endpoint/data_loaders/index_endpoint_rule_alerts.ts

@@ -127,14 +127,17 @@ const ensureEndpointRuleAlertsIndexExists = async (esClient: Client): Promise<vo
     indexMappings.mappings._meta.kibana.version = kibanaPackageJson.version;
   }
 
+  const doesIndexExist = await esClient.indices.exists({ index: indexMappings.index });
+
+  if (doesIndexExist) {
+    return;
+  }
   try {
     await esClient.indices.create({
       index: indexMappings.index,
-      body: {
-        settings: indexMappings.settings,
-        mappings: indexMappings.mappings,
-        aliases: indexMappings.aliases,
-      },
+      settings: indexMappings.settings,
+      mappings: indexMappings.mappings,
+      aliases: indexMappings.aliases,
     });
   } catch (error) {
     // ignore error that indicate index is already created

x-pack/test/security_solution_endpoint/apps/endpoint/responder.ts

@@ -81,8 +81,7 @@ export default ({ getPageObjects, getService }: FtrProviderContext) => {
     );
   };
 
-  // Failing: See https://github.com/elastic/kibana/issues/139260
-  describe.skip('Response Actions Responder', function () {
+  describe('Response Actions Responder', function () {
     let indexedData: IndexedHostsAndAlertsResponse;
     let endpointAgentId: string;
 
@@ -183,6 +182,11 @@ export default ({ getPageObjects, getService }: FtrProviderContext) => {
         // Show event/alert details for the first one in the list
         await pageObjects.timeline.showEventDetails();
 
+        // TODO: The index already exists error toast should not show up
+        // close and dismiss it if it does
+        if (await testSubjects.exists('globalToastList')) {
+          await testSubjects.click('toastCloseButton');
+        }
         // Click responder from the take action button
         await testSubjects.click('take-action-dropdown-btn');
         await testSubjects.clickWhenNotDisabled('endpointResponseActions-action-item');