Fixes Failing test: Jest Integration Tests.x-pack/platform/plugins/sh…

…ared/task_manager/server/integration_tests - unrecognized task types should be no workload aggregator errors when there are removed task types (elastic#210399)

Resolves elastic#208459

## Summary

The fix added in this
[PR](elastic#206598) to call the
`mark_removed_tasks_as_unrecognized` tasks sometimes throws an error if
the task is in the middle of running. This PR adds a try/catch and a
retry to the `runSoon` call.

---------

Co-authored-by: Elastic Machine <elasticmachine@users.noreply.github.com>
(cherry picked from commit 5500eab)

x-pack/platform/plugins/shared/task_manager/server/integration_tests/removed_types.test.ts

@@ -28,8 +28,7 @@ jest.mock('../monitoring/workload_statistics', () => {
   };
 });
 
-// FLAKY: https://github.com/elastic/kibana/issues/208459
-describe.skip('unrecognized task types', () => {
+describe('unrecognized task types', () => {
   let esServer: TestElasticsearchUtils;
   let kibanaServer: TestKibanaUtils;
   let taskManagerPlugin: TaskManagerStartContract;
@@ -114,8 +113,16 @@ describe.skip('unrecognized task types', () => {
     taskIdsToRemove.push(notRegisteredTypeId);
 
     // To be sure that the background task that marks removed tasks as unrecognized has run after the tasks were created
-    const runSoonResponse = await taskManagerPlugin.runSoon('mark_removed_tasks_as_unrecognized');
-    expect(runSoonResponse).toEqual({ id: 'mark_removed_tasks_as_unrecognized' });
+    await retry(async () => {
+      try {
+        const runSoonResponse = await taskManagerPlugin.runSoon(
+          'mark_removed_tasks_as_unrecognized'
+        );
+        expect(runSoonResponse).toEqual({ id: 'mark_removed_tasks_as_unrecognized' });
+      } catch (err) {
+        // ignore errors and retry
+      }
+    });
 
     await retry(async () => {
       const task = await getTask(kibanaServer.coreStart.elasticsearch.client.asInternalUser);