Update citation and changelog for version 2.12 (ESMValGroup#3945)

Update the version number and release notes for v2.11.0 (ESMValGroup#…

…3695)

Update `scipy.integrate.simps` import (ESMValGroup#3704)

Update release date

Add release notes for v2.9 (ESMValGroup#3266)

Co-authored-by: Valeriu Predoi <[email protected]>
Co-authored-by: Rémi Kazeroni <[email protected]>

Draft changelog for `v2.8.0` (ESMValGroup#3124)

Co-authored-by: Axel Lauer <[email protected]>

up version to 270 in CITATION

Increase ESMValTool version to 2.6.0 (ESMValGroup#2738)

* Edit CITATION.cff for version 2.6

* Change date

Final update of changelog for v2.5.0 (ESMValGroup#2601)

Update changelog for 2.4.0 release (ESMValGroup#2411)

* First draft of changelog

* Update missing labels on PRs

* Remove duplicates from previous release

* Final cleaning of PRs

* Add highlights

* Add changelog PR to changelog