Python 3.10.12 fixes some CVEs for which Dangerzone does not appear to be
affected, however its binaries are not made available by the python
foundation. Moving to 3.11 should be trivial since this was already
deployed in Fedora 37+.
The Ubuntu 23.04 docker image includes a user by default (ubuntu) which
overtakes the 1000 uid and so our user becomes 1001 which makes the user
directory unwritable. The solution as suggested in [1] was to remove
that user.
[1]: https://bugs.launchpad.net/cloud-images/+bug/2005129Fixes#452
Update our GitHub Actions workflow with the following tests:
1. Build a .deb for Dangerzone on Debian Bookworm.
2. Install this .deb on every Debian-based platform that we support.
3. Test that the installed version runs successfully.
This way, we can be sure that .deb that we create on a single Debian
version (here we choose Debian Bookworm) works on all platforms.
Refs #358
Adds tests for macOS and Windows with the dummy converter. Tests won't
actually perform the conversion. But it should be enough for us to test
the remainder of the codebase.
Fixes#229
