[Controls] Fix flaky a11y test (elastic#169559)

Closes elastic#169542

## Summary

For some reason, the search session popover was being opened, which
blocked the controls button from being clickable:


![image](https://github.com/elastic/kibana/assets/8698078/6882e67e-6f17-4820-8e71-14e84c3d04c2)

I'm unsure why this popover is open to begin with; this should **only**
happen when the `searchSessionIndicator` button is clicked, but this
button is **not** interacted with in **any** of the accessibility tests
(that I could find). This makes me suspicious that this is actually a
**misclick** - i.e. the element that was meant to be clicked gets moved
(possibly the Dashboard "edit" button?), which causes the
`searchSessionIndicator` button to be clicked instead.

Going off this theory, I've switched the controls `a11y` tests to use
the Dashboard page's methods (which have more safeguards in place) to
navigate to the desired dashboard rather than clicking elements solely
based off of the `data-test-subj` like we were previously.

### [Flaky Test
Runner](https://buildkite.com/elastic/kibana-flaky-test-suite-runner/builds/3686)


![image](https://github.com/elastic/kibana/assets/8698078/74fb0d27-9cb2-4650-ba91-97865a3bd962)

### Checklist

- [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


### 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/accessibility/apps/dashboard_controls.ts

@@ -23,8 +23,8 @@ export default function ({ getService, getPageObjects }: FtrProviderContext) {
       });
       await PageObjects.home.addSampleDataSet('flights');
       await PageObjects.common.navigateToApp('dashboard');
-      await testSubjects.click('dashboardListingTitleLink-[Flights]-Global-Flight-Dashboard');
-      await testSubjects.click('dashboardEditMode');
+      await PageObjects.dashboard.loadSavedDashboard('[Flights] Global Flight Dashboard');
+      await PageObjects.dashboard.switchToEditMode();
     });
 
     after(async () => {