Release candidate 1 for bugfix release v2.8.1

This is RC1 for a potential bugfix release v2.8.1 - it is meant to be used for testing by @remi-kazeroni with ESMValTool, and detect any issues that may arise from various code changes and dependency pins/changes due to the newly introduced support for Python=3.11. 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.