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Changes:
* Drop EOL python 3.6 / 3.7. PR 1129, 1160.
* Add support for python 3.12. PR 1147, 1148, 1152, 1153, 1154, 1163,
1164, 1165, 1166, 1176, 1177, 1182.
* E721: adjust handling of type comparison. Allowed forms are now
``isinstance(x, t)`` or ``type(x) is t``. PR 1086, 1167.
* Remove handling of python 2 ``<>`` operator. PR 1161.
* W606: removed. ``async`` / ``await`` are always keywords. PR 1162.
* Internal: move tests to pytest. PR 1168, 1169, 1171, 1173, 1174, 1175.
* Remove handling of python 2 ``ur''`` strings. PR 1181.