[Dashboard] Unskip flaky colour sync test (#173582)

Closes #148557

## Summary

[Ran the
FTR](https://buildkite.com/elastic/kibana-flaky-test-suite-runner/builds/4636)
on the skipped test suite and it passed 100 times... Really unclear on
why it keeps failing, especially after
#172633. For now, since I can't
get it to fail locally or with the FTR, I'm going to unskip. If it
starts to fail on `main` again, we could loop in the Vis team to help
(since it's the timepicker in the Lens app that is misbehaving) - but
hopefully the previous failure was a fluke and that won't be necessary🤞

### Checklist

- [x] [Flaky Test
Runner](https://ci-stats.kibana.dev/trigger_flaky_test_runner/1) was
used on any tests changed
([Link](https://buildkite.com/elastic/kibana-flaky-test-suite-runner/builds/4636))
![Screenshot 2023-12-20 at 7 47
58 AM](https://github.com/elastic/kibana/assets/8698078/523e715a-a347-4c82-955c-b18cabe53566)


### For maintainers

- [ ] This was checked for breaking API changes and was [labeled
appropriately](https://www.elastic.co/guide/en/kibana/master/contributing.html#kibana-release-notes-process)

x-pack/test/functional/apps/dashboard/group2/sync_colors.ts

@@ -35,8 +35,7 @@ export default function ({ getService, getPageObjects }: FtrProviderContext) {
     return colorMapping;
   }
 
-  // FLAKY: https://github.com/elastic/kibana/issues/148557
-  describe.skip('sync colors', function () {
+  describe('sync colors', function () {
     before(async function () {
       await esArchiver.loadIfNeeded('x-pack/test/functional/es_archives/logstash_functional');
       await kibanaServer.importExport.load(