Skip Serverless Transaction groups alerts when data is loaded with av…

…g transaction duration alerts returns the correct number of alert counts (elastic#201533)

## Summary
Related to elastic#201531

This PR skips `Transaction groups alerts when data is loaded with avg
transaction duration alerts returns the correct number of alert counts`,
which is inside
`x-pack/test/api_integration/deployment_agnostic/apis/observability/apm/transactions/transactions_groups_alerts.spec.ts`
file, as it's failing on MKI.

x-pack/test/api_integration/deployment_agnostic/apis/observability/apm/transactions/transactions_groups_alerts.spec.ts

@@ -73,7 +73,10 @@ export default function ApiTest({ getService }: DeploymentAgnosticFtrProviderCon
     return response.body as TransactionsGroupsMainStatistics;
   }
 
-  describe('Transaction groups alerts', () => {
+  describe('Transaction groups alerts', function () {
+    // fails on MKI, see https://github.com/elastic/kibana/issues/201531
+    this.tags(['failsOnMKI']);
+
     describe('when data is loaded', () => {
       const transactions = [
         {