…ted as integers

Prior to pythongh-11952, several standard library functions that expected
integer arguments would nevertheless silently accept (and truncate)
non-integer arguments. This behaviour was deprecated in pythongh-11952, and
removed in pythongh-15636.

However, it may be possible to interpret some non-integer numeric types
(such as `decimal.Decimal`s) as integers if they contain no fractional
part. Implement `__index__` for `decimal.Decimal`, returning an integer
representation of the value if it does not contain a fractional part or
raising a `TypeError` if it does.

`datetime` used to accept objects that implement `__int__` or `__index__`, but in Python 3.10 it was changed to accept only `__index__`.
python/cpython#15636

* hightime: Update Python versions in tox.ini

* hightime: Update trove classifiers

* hightime: More tox.ini updates

* hightime: Use __index__ instead of __int__

`datetime` used to accept objects that implement `__int__` or `__index__`, but in Python 3.10 it was changed to accept only `__index__`.
python/cpython#15636

* github: Update Python versions