Wait for backfill SOs to be deleted before running the invalidate API…

… key task (elastic#198422)

Resolves elastic#198168

Flaky test runners:
-
https://buildkite.com/elastic/kibana-flaky-test-suite-runner/builds/7309
-
https://buildkite.com/elastic/kibana-flaky-test-suite-runner/builds/7314

(cherry picked from commit 7b05079)

x-pack/test/alerting_api_integration/security_and_spaces/group1/tests/alerting/backfill/api_key.ts

@@ -252,6 +252,17 @@ export default function apiKeyBackfillTests({ getService }: FtrProviderContext)
         expect(e?.event?.outcome).to.eql('success');
       }
 
+      // wait for all the ad hoc run SO to be deleted
+      await retry.try(async () => {
+        try {
+          // throws when not found
+          await getAdHocRunSO(backfillId);
+          throw new Error('should have thrown');
+        } catch (e) {
+          expect(e.message).not.to.eql('should have thrown');
+        }
+      });
+
       // invoke the invalidate task
       await runInvalidateTask();