Display "exception" logs as level "error"

[kimsappi]

Summary

Changes the displayed log level added by the add_log_level processor for logs using the exception() method to "error" instead of "exception". This replicates the behaviour of CPython and structlog pre-23.3.0 (#572).

This issue has been discussed in #584.

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[hynek]

Looks good to you @bcdickinson?

[albertferras-vrf]

Looking forward for this fix. Will you release a hotfix (23.3.1) just with this?

[hynek]

No, there’s gonna be a 24.1 soon-ish, there’s been a bunch of other smaller fixes.