Specify Debian version (#105)

On 2023-06-14, Docker updated the default Debian Linux version in its
Python official images from Debian bullseye to Debian bookworm.
As inboard uses the default Debian Linux version from the Docker Python
official images, this meant that the next release of inboard
(0.50.0 - 2023-06-22) automatically updated to bookworm. There were some
[issues](https://github.com/docker-library/python/issues?q=bookworm)
noted by the community after this update.

inboard will now specify the Debian version when building Docker images.
The current Debian version is still Debian 12 ("bookworm").
The next Debian version, Debian 13 ("trixie") does not have a release
date yet, but inboard will update to trixie when it is stable and will
provide a new release after the update.

https://github.com/docker-library/python
#80
https://inboard.bws.bio/changelog#0510-2023-07-09

.github/workflows/ci.yml

@@ -124,7 +124,7 @@ jobs:
     strategy:
       fail-fast: false
       matrix:
-        linux-version: ["", "alpine", "slim"]
+        linux-version: ["alpine", "bookworm", "slim-bookworm"]
         python-version: ["3.8", "3.9", "3.10", "3.11", "3.12"]
     steps:
       - uses: actions/checkout@v4