Build pop-up: show error notification if the build has failed

I think these pop ups are cool. However, it doesn't provide too much extra useful information that the list item. The extra information it provides that's not in the list item is the commit (6225c4b5) and the build time (45 seconds). All the other data it shows in the list item:

I think we can take advantage of this popup and add the reason for the build to fail here, for example. That way, users don't have to jump into the build details page to understand what happened:

We could pull the error notifications and show them inside the popup. In this particular case, it would show: No HTML content found -- No content was output to the path "$READTHEDOCS_OUTPUT/html". Read more about where to put your built files.

Start by locating the build pop-up and the source of build error notifications. Update the pop-up so failed builds display the relevant error reason and its accompanying guidance, rather than requiring users to open the build details page. Done means the failure message shown in the issue appears in the pop-up.