[PATCH] Use dbus-run-session to run D-Bus tests instead of dbus-launch

[PATCH] Use dbus-run-session to run D-Bus tests instead of dbus-launch

dbus-run-session spawns a session that gets terminated automatically
after the execution of the command. It is a simpler way compared to
dbus-launch, which relies on the X11 tolaunching (which would explain
why it is not used on macOS, as the comment says).

Hence, use dbus-run-session instead of dbus-launch to run each D-Bus
test. Keep the existing macOS behaviour as-is for now, adding a comment
to test using dbus-run-session in the future.

Gbp-Pq: Name upstream_Use-dbus-run-session-to-run-D-Bus-tests-instead-of-d.patch