[ML] Functional tests - re-activate date_nanos test (#59649)

This PR re-activates the date_nanos functional UI test.

Author: pheyos

x-pack/test/functional/apps/machine_learning/anomaly_detection/date_nanos_job.ts

@@ -165,8 +165,7 @@ export default function({ getService }: FtrProviderContext) {
     },
   ];
 
-  // test failures, see #59419
-  describe.skip('job on data set with date_nanos time field', function() {
+  describe('job on data set with date_nanos time field', function() {
     this.tags(['smoke', 'mlqa']);
     before(async () => {
       await esArchiver.load('ml/event_rate_nanos');