Bump container base image to Python 3.12

[danielballan]

Checklist

• [x] Add a Changelog entry
• [ ] Add the ticket number which this PR closes to the comment section

[danielballan]

There is no particular reason to do this now; this is just general housekeeping. We may see some performance improvements, as Python 3.12 is generally faster than 3.11.

[danielballan]

The container canary failed twice in a row, so there may be a real issue there.

[danielballan]

Superseded by #781. This problem was canary here was simply that we were not waiting long enough for the container to start.