Show warnings in logs

[schlunma]

Description

We use logging.captureWarnings in our logging configuration to show warnings emitted by the warnings module as logging messages. According to the docs, this does the following:

If capture is True, warnings issued by the warnings module will be redirected to the logging system. Specifically, a warning will be formatted using warnings.formatwarning() and the resulting string logged to a logger named 'py.warnings' with a severity of WARNING.

Note the logger name py.warnings. Since #2765, we only show messages from certain loggers. However, the py.warnings logger is missing here, which eventually leads to omitted warnings messages.

This PR adds this. In addition, one instance of a DeprecationWarning is changed to ESMValCoreDeprecationWarning to be consistent with other deprecations.

Closes #3213.

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 96.46%. Comparing base (8c8ce25) to head (1b0aa0b).

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3214      +/-   ##
==========================================
- Coverage   96.48%   96.46%   -0.02%     
==========================================
  Files         281      281              
  Lines       16317    16317              
==========================================
- Hits        15743    15740       -3     
- Misses        574      577       +3     

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[bouweandela]

Thanks!