Force back to Bullseye images

Moulrequested to merge
7_back_to_bullseye into master

since we can’t use Bookworm images with our runner yet

https://github.com/docker-library/python/issues/837#issuecomment-1599640563

Revert "Remove '-bullseye' from the images tags (#7 (closed))"

This somehow reverts commit 71ced44b.

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