Fix CHANGELOG generation in the presence of RCs

[vados-cosmonic]

Right now, when generating/updating the CHANGELOG for a release, only the commits up until the latest tag are included.

This generally works for going from a release tag to a release tag (ex. 0.1.0 -> 0.2.0 or 0.1.0 -> 0.1.1), but this does not work as well for going from something like 0.2.0-rc.0 to 0.2.0, when 0.2.0-rc.0, 0.2.0-rc.1, 0.2.0-rc.2 (and so forth) exist.

The commits from all the RCs up until the previous non-RC tag should be included, but aren't -- so the CHANGELOG ends up being only the latest RC's changed commits (which could be empty, if we made another RC without making any changes for some reason).

[vados-cosmonic]

This has been fixed as of this commit