python-pydantic-v1: Handle response chartset in exception.

[igorgatis]

This PR fixes the issue https://github.com/OpenAPITools/openapi-generator/issues/19862.

Currently, the generated code for python-pydantic-v1 tries to decode the response using utf-8. This fails when the response uses character sequence that is not utf-8, like so:

  File ".../.venv/lib/python3.11/site-packages/my_api/api_client.py", line 219, in __call_api
    e.body = e.body.decode('utf-8')
             ^^^^^^^^^^^^^^^^^^^^^^
UnicodeDecodeError: 'utf-8' codec can't decode byte 0xe7 in position 78: invalid continuation byte

This change tries to use charset from the response. It leaves content unchanged when decoding fails.

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[igorgatis]

@fa0311 @multani