When the current release is e.g. 0.40.0, then we don't show 0.40 in the "previous releases" sidebar. That makes sense because the user is already on the current release.

But if the current release is a patch version, like 0.42.1, then we show 0.42 in the previous releases sidebar. Even though a new patch version should be on the same branch of stable/0.42 docs.

Probably requires a tweak to versionutils.py.