ESMValCore v2.8.1 release

[bouweandela]

Manager	Buddy	Feature Freeze	Milestone	Release notes
@valeriupredoi	@remi-kazeroni	-	-	v2.8.1

Minor Release	Status	Date	RTD	Release	conda-forge	PyPI	DockerHub
v2.8.1rc1		2023-05-19	Docs	v2.8.1rc1	esmvalcore_rc	esmvalcore (--pre)	docker
v2.8.1rc2		2023-06-01	Docs	v2.8.1rc2	esmvalcore_rc	esmvalcore (--pre)	docker
v2.8.1		2023-06-02	Docs	v2.8.1	esmvalcore	esmvalcore	docker

[bouweandela]

Recipe testing results available in #2069.