[tests] skip advanced_settings for MKI run (elastic#172682)

## Summary

Skipping advanced settings tests for MKI pipeline as we see many random
failures:


https://buildkite.com/elastic/appex-qa-serverless-kibana-ftr-tests/builds/599

https://buildkite.com/elastic/appex-qa-serverless-kibana-ftr-tests/builds/600

I was trying to make a quick fix but I don't see a clear reason for this
failure in
```
      it('allows resetting a setting to its default value', async () => {
        const fieldTestSubj = 'management-settings-editField-' + settings.CSV_QUOTE_VALUES_ID;
        const resetLinkTestSubj = 'management-settings-resetField-' + settings.CSV_QUOTE_VALUES_ID;
        expect(await testSubjects.exists(resetLinkTestSubj)).to.be(true);
        await testSubjects.click(resetLinkTestSubj);

        // Save changes
        await testSubjects.click(SAVE_BUTTON_TEST_SUBJ);

        await browser.refresh();
        await pageObjects.common.sleep(1000);

        // Check if field is now enabled
        expect(await testSubjects.isEuiSwitchChecked(fieldTestSubj)).to.be(true);
      });
```

and we don't see it failing in Kibana CI with local Kibana build

x-pack/test_serverless/functional/test_suites/common/management/advanced_settings.ts

@@ -38,6 +38,8 @@ export default ({ getPageObjects, getService }: FtrProviderContext) => {
   let INITIAL_CSV_QUOTE_VALUES_SETTING_VALUE: any;
 
   describe('Common advanced settings', function () {
+    // the suite is flaky on MKI
+    this.tags(['failsOnMKI']);
     before(async () => {
       // We need kibana_admin role in order to update settings
       await security.testUser.setRoles(['kibana_admin']);