[Infra] Attempt to fix APMEventClient unit test (elastic#191268)

closes [190703](elastic#190703)

## Summary

I'm not sure if this change will resolve the flakiness. What I
discovered is that the test had an open handle due to an unfinished
promise.

Co-authored-by: Elastic Machine <elasticmachine@users.noreply.github.com>

x-pack/plugins/observability_solution/apm_data_access/server/lib/helpers/create_es_client/create_apm_event_client/index.test.ts

@@ -36,7 +36,9 @@ describe('APMEventClient', () => {
         esClient: {
           search: async (params: any, { signal }: { signal: AbortSignal }) => {
             abortSignal = signal;
-            await setTimeoutPromise(3_000);
+            await setTimeoutPromise(3_000, undefined, {
+              signal: abortSignal,
+            });
             return {};
           },
         } as any,