Upstream: https://we.phorge.it/T16338

Steps to replicate the issue

1. Visit the Wikidata project workboard.
2. Attempt to scroll down the left-hand sidebar.

What happens?
The entire page, including the workboard columns, scroll.
This means that you can't e.g. look at/use the links in the lower part of the sidebar, while also looking at the majority of the workboard itself.

Screen recording: F70059228

What should have happened instead?
As there is no content underneath the workboard columns, they presumably shouldn't scroll - presumably only the left-hand sidebar should be scrolling here.

Other information/Notes
For me, this seems to be solved/worked-around with the addition of the following CSS (similar to what's used for the workboard columns themselves; but hopefully avoiding an issue like T255859, due to the fact that the Phabricator header is hopefully not liable to have different heights depending on which workboard page is being viewed). I don't feel confident enough to formally propose this e.g. upstream, though, as I'm not sure e.g. whether it'd lead to any unintended consequences.

.phui-profile-menu .project-board-nav .phabricator-side-menu {
    max-height: calc(100vh - 56px);
    overflow-y: auto;
}

F70059364 is a screen recording of how the workboard sidebar scrolls on its own with this CSS in place.