longintrepr.h: No such file or directory, on Python 3.11

I upgraded a server from Debian 11 to 12, which comes standard with Python 3.11, under which this happens:

Fails to build on Python 3.11 - longintrepr.h: No such file or directory

Cue learning about pyenv, and updating pyproject.toml of all the FastAPI microservices to make them capable of “poetry run” on Python 3.9.

Then again, all 5 microservices had been running without any intervention for almost one year.

Not bad. Not bad at all.