Accessibility: Keyboard focus is not coming on the horizontal scrollbar of Request and Response Samples

[arlina-espinoza]

Describe the bug
When the request or response sample text overflows the width of the container, a horizontal scrollbar appears.
If the request/response does not contains a "focusable" element, then the user can't use the left and right arrow keys to view the rest of the code in that section.

Expected behavior
If the request/response sections present a scrollbar, they should be keyboard accessible.

How to reproduce

1. On Chrome (not sure about other browsers).
2. Go to example page, POST Buy museum tickets method: https://redocly.github.io/redoc/#tag/Tickets/operation/buyMuseumTickets
3. Resize browser window to a small width, so that the "Request samples" of the method shows a horizontal scrollbar.
4. Try tabbing to get to the "Request samples" and use right/left arrow keys to focus. It is not possible.

Screenshots

Additional context
For this bug, the request/response text does not need to have any focusable elements (like JSON expand/collapse buttons). The method referred in "how to reproduce" is an example that should display the bug.

Solution
Add tabindex="0" to the element that has the scrollbar.