[TSVB] Stabilize flaky TSVB test (#167848)

## Summary

Closes https://github.com/elastic/kibana/issues/167791

https://buildkite.com/elastic/kibana-flaky-test-suite-runner/builds/3282
Flaky runner (50 times)


### 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

test/functional/page_objects/visual_builder_page.ts

@@ -663,6 +663,7 @@ export class VisualBuilderPageObject extends FtrService {
    * @memberof VisualBuilderPage
    */
   public async setFieldForAggregation(field: string, aggNth: number = 0): Promise<void> {
+    await this.visChart.waitForVisualizationRenderingStabilized();
     const fieldEl = await this.getFieldForAggregation(aggNth);
 
     await this.comboBox.setElement(fieldEl, field);