[Discover] Fix flaky test elastic#217012 (elastic#218021)

## Summary

Flaky test runner x100:
https://buildkite.com/elastic/kibana-flaky-test-suite-runner/builds/8175.

Resolves elastic#217012.

### Checklist

- [ ] Any text added follows [EUI's writing
guidelines](https://elastic.github.io/eui/#/guidelines/writing), uses
sentence case text and includes [i18n
support](https://github.com/elastic/kibana/blob/main/src/platform/packages/shared/kbn-i18n/README.md)
- [ ]
[Documentation](https://www.elastic.co/guide/en/kibana/master/development-documentation.html)
was added for features that require explanation or tutorials
- [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
- [ ] If a plugin configuration key changed, check if it needs to be
allowlisted in the cloud and added to the [docker
list](https://github.com/elastic/kibana/blob/main/src/dev/build/tasks/os_packages/docker_generator/resources/base/bin/kibana-docker)
- [ ] This was checked for breaking HTTP API changes, and any breaking
changes have been approved by the breaking-change committee. The
`release_note:breaking` label should be applied in these situations.
- [x] [Flaky Test
Runner](https://ci-stats.kibana.dev/trigger_flaky_test_runner/1) was
used on any tests changed
- [ ] The PR description includes the appropriate Release Notes section,
and the correct `release_note:*` label is applied per the
[guidelines](https://www.elastic.co/guide/en/kibana/master/contributing.html#kibana-release-notes-process)

Author: davismcphee

src/platform/test/functional/apps/discover/group1/_discover_accessibility.ts

@@ -50,8 +50,7 @@ export default function ({ getService, getPageObjects }: FtrProviderContext) {
       await kibanaServer.savedObjects.clean({ types: ['search', 'index-pattern'] });
     });
 
-    // FLAKY: https://github.com/elastic/kibana/issues/217012
-    describe.skip('top nav menu buttons', () => {
+    describe('top nav menu buttons', () => {
       const focusAndPressButton = async (buttonTestSubject: string | WebElementWrapper) => {
         const button =
           typeof buttonTestSubject === 'string'
@@ -68,7 +67,8 @@ export default function ({ getService, getPageObjects }: FtrProviderContext) {
         await retry.try(async () => {
           expect(await hasFocus(menuButtonTestSubject)).to.be(false);
         });
-
+        // Small delay to allow the overlay to open fully
+        await new Promise((resolve) => setTimeout(resolve, 500));
         await browser.pressKeys(browser.keys.ESCAPE);
         await retry.try(async () => {
           expect(await hasFocus(menuButtonTestSubject)).to.be(true);