A hotfix release for Trixie environments

On Debian Trixie and derivatives, when some specific Qt6 packages are
installed and not some other ones, due to how we fallback import
mechanism is implemented, a bug can happen making it impossible for
Dangerzone to be launched.

This 0.9.1 hotfix release fixes this error by depending explicitely on
the Pyside6 dependencies if they are installeable on the system.

Release for v0.9.1

First Release Candidate for 0.9.1

First Release Candidate for 0.9.0