[Docs Bug] Virtual assistant pop-up fully covers button to return to top

### Link to the page(s) on docs.getdbt.com requiring updates

# Bug
The "Virtual Assistant Chat" iframe nearly completely covers the "Scroll back to top" button on the bottom right of **any** page.

## How to replicate
#### Open any page on docs.getdbt.com, let's say https://docs.getdbt.com/reference/resource-configs/docs .
The chat pop-up appears as expected

#### Scroll down the page
The "Scroll back to top" button appears as expected, however it is mostly covered by the chat pop-up:

#### After deleting the chat pop-up
Functional "Scroll back to top" button" is able to be interacted with again

## Proposed fix
Have them next to each other, or stacked

### Tell us more about this update

The chat covering the "Scroll back to top" button is quite annoying on very long pages, and is a visual distraction on top of it.
This issue is present on all pages of docs.getdbt.com where the content is scrollable

### Reviewers/Stakeholders/SMEs

I have no idea who should review this

### Related GitHub issues

_No response_

### Additional information

_No response_