app: Fix compiler errors with old libpolkit
app: Fix compiler errors with old libpolkit

Make sure we have g_autoptr support for libpolkit types even if we're
compiling against an old version of libpolkit, the same way we do in
system-helper/flatpak-system-helper.c.

Fixes https://github.com/flatpak/flatpak/issues/2401

Closes: #2403
Approved by: matthiasclasen

matthiasclasen/flatpak,flatpak/flatpak,flatpak/flatpak,matthiasclasen/flatpak,matthiasclasen/flatpak,matthiasclasen/flatpak,flatpak/flatpak,flatpak/flatpak,flatpak/flatpak,matthiasclasen/flatpak