Skip UA tests when running fwd-compatibility tests (elastic#204650)

## Summary

Resolves elastic#204520

Reasoning in
elastic#204520 (comment)


### 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

x-pack/test/api_integration/apis/upgrade_assistant/index.ts

@@ -5,10 +5,25 @@
  * 2.0.
  */
 
+import { version as kibanaVersion } from '../../../../../package.json';
 import { FtrProviderContext } from '../../ftr_provider_context';
 
-export default function ({ loadTestFile }: FtrProviderContext) {
+export default function ({ loadTestFile, getService }: FtrProviderContext) {
   describe('Upgrade Assistant', function () {
+    const es = getService('es');
+
+    before(
+      "Check version to avoid failures during forward-compatibility tests where these don't make sense",
+      async function () {
+        const {
+          version: { number: esVersion },
+        } = await es.info();
+        if (esVersion.replace('-SNAPSHOT', '') !== kibanaVersion.replace('-SNAPSHOT', '')) {
+          this.skip();
+        }
+      }
+    );
+
     loadTestFile(require.resolve('./upgrade_assistant'));
     loadTestFile(require.resolve('./cloud_backup_status'));
     loadTestFile(require.resolve('./privileges'));