[BUG] F-Droid - upgrade to Java 21

[licaon-kter]

Since January we use Debian Trixie with Java 21 by default

Any chance you can update your local tooling too?

[deltazefiro]

Sure! Next release will build with Java 21. Do I need to update the F-Droid build config?

[licaon-kter]

ping us when tagged