[ML] Functional tests: unskip forecast flaky test (#187906)

## Summary

Fixes #186091
Backport for #187795

Investigation indicated something in the testing environment - likely
the chrome version. That has been updated since so letting the CI run to
confirm

Flaky test runner build
https://buildkite.com/elastic/kibana-flaky-test-suite-runner/builds/6498


### Checklist

Delete any items that are not applicable to this PR.

- [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
- [ ] [Flaky Test
Runner](https://ci-stats.kibana.dev/trigger_flaky_test_runner/1) was
used on any tests changed

Co-authored-by: Elastic Machine <[email protected]>

x-pack/test/functional/apps/ml/anomaly_detection/forecasts.ts

@@ -39,8 +39,7 @@ export default function ({ getService }: FtrProviderContext) {
   const esArchiver = getService('esArchiver');
   const ml = getService('ml');
 
-  // Failing: See https://github.com/elastic/kibana/issues/186091
-  describe.skip('forecasts', function () {
+  describe('forecasts', function () {
     this.tags(['mlqa']);
 
     describe('with single metric job', function () {