Prevent reloading iframe in the block config popup when opening Universal Discovery to embed a content in the block.

Steps to reproduce:
1. Open a landing page with embed blocks in it or create a new one and add an embed block onto it,
2. Open block settings,
3. Click on Embed button (currently called Button),
4. Pick any content,
5. Confirm.

Expected result:
The config form is visible.

Actual result:
The config form disappeared.