Attempt at supporting Python 3.12

[bouweandela]

Description

See #2228

Closes #issue_number

Link to documentation:

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[codecov[bot]]

Codecov Report

Attention: Patch coverage is 0% with 1 lines in your changes are missing coverage. Please review.

Project coverage is 94.51%. Comparing base (515f399) to head (dcf2dc6).

Files	Patch %	Lines
esmvalcore/_task.py	0.00%	1 Missing :warning:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #2437 +/- ## ======================================= Coverage 94.51% 94.51% ======================================= Files 246 246 Lines 14024 14024 ======================================= Hits 13255 13255 Misses 769 769 ```

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[bouweandela]

@valeriupredoi This seems to work: tests are passing and I can run prospector.