Release candidate 2 for bugfix release v2.8.1

This release candidate 2 (rc2) comes on the back of rc1, but we removed the explicit need for the vectorized module of shapely in the environment files. This allows installing a newer version of shapely as well as it fixes the call to the esmvaltool executable. We will update the Changelog when/if we decide to release a bugfix release v2.8.1. You can use this packaged RC with ESMValTool once it gets deployed to the rc channel of conda.