[Merge after v2.11.0 Release] Retire support for Python 3.9

[valeriupredoi]

Description

• Closes #3681
• Link to documentation: PR3683

Standard procedure to retire support for Python 3.9, similar to https://github.com/ESMValGroup/ESMValCore/pull/2447

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[valeriupredoi]

@bouweandela this :sauropod: too :beer:

[valeriupredoi]

Could you also update environment_osx.yml please?

Ouch! Have I missed it - on it now :green_apple: - done in 7c50fa9a35a273890c12ecd5fc4abb2e1e654edd

[valeriupredoi]

Cheers, buds 🍺