bluetooth: Adapt to new GnomeBluetooth library in GNOME Shell 42

GNOME 42 has a new version of the GnomeBluetooth library, with a
different API. Adjust to this.

Signed-off-by: Simon McVittie <smcv@debian.org>
Resolves: https://github.com/bjarosze/gnome-bluetooth-quick-connect/issues/53