Classic Editor on Simple Sites: category list should have vertical scroll

[mrfoxtalbot]

Quick summary

On the Classic editor, the list of categories should have vertical scroll to prevent it from being too tall if the site has a large number of categories.

https://github.com/Automattic/wp-calypso/assets/4452464/2a79c817-682f-41b8-8361-7ceb441870ce

On dotcom simple sites, there is no vertical scroll. Atomic sites work as expected (just like self-hosted ones).

https://github.com/Automattic/wp-calypso/assets/4452464/6b9d1122-c22e-4a74-a77f-115485edd0b9

Steps to reproduce

1. Go to a simple site that has 15+ terms
2. Create a new post using the classic editor
3. Look at the categories box

What you expected to happen

It should have scroll, just like in core

What actually happened

The category box extends vertically (no scroll)

Impact

All

Available workarounds?

We can direct users to install a custom CSS browser extension and add the following CSS:

.categorydiv div.tabs-panel {
  max-height: 200px;
    overflow: auto;
}

Platform (Simple and/or Atomic)

Simple

Logs or notes

More context in 8339518-zd-a8c