Build broke on Python 3.11

[gilch]

The offending change was #205 due to a bad regex using an (?m) flag not at the start. This form had been deprecated and was removed in python/cpython#91222

For those installing master from GitHub, you'll have to use Python 3.8-3.10 or install from earlier commit until I get this fixed (relatively soon).

Fixing the broken line will be easy, but the automation should have caught it. I at least expected a deprecation warning, but maybe I don't have them properly turned on when running tests. Needs more investigation. Python has been going through rolling deprecations and removals lately.

If the warnings prove inadequate, I'm considering doing builds on multiple versions of Python (currently 3.8-3.11). I wonder if there's an easy way to do that in the test-package.yml or if I have to figure out Tox.

I'll also upgrade to 3.9 when 3.8 reaches end-of-support next year. I'm behind the curve to support other Python implementations which tend to lag behind CPython by varying degrees. I'd still be on 3.7 through June but needed features early from 3.8.