unit/test-gdbus-client: Fix memory leak on client_no_object_manager
unit/test-gdbus-client: Fix memory leak on client_no_object_manager

When creating a proxy manually with g_dbus_proxy_new it has to be freed
with g_dbus_proxy_unref otherwise it leaks:

395 (80 direct, 315 indirect) bytes in 1 blocks are definitely lost in loss record 800 of 834
   at 0x4C29BCF: malloc (in /usr/lib64/valgrind/vgpreload_memcheck-amd64-linux.so)
   by 0x4E84575: g_try_malloc0 (in /usr/lib64/libglib-2.0.so.0.4200.2)
   by 0x40E244: proxy_new (client.c:411)
   by 0x40F7FD: g_dbus_proxy_new (client.c:485)
   by 0x405844: client_no_object_manager (test-gdbus-client.c:837)
   by 0x410882: run_callback (tester.c:413)
   by 0x4E7E7FA: g_main_context_dispatch (in /usr/lib64/libglib-2.0.so.0.4200.2)
   by 0x4E7EB97: ??? (in /usr/lib64/libglib-2.0.so.0.4200.2)
   by 0x4E7EEC1: g_main_loop_run (in /usr/lib64/libglib-2.0.so.0.4200.2)
   by 0x411CF1: tester_run (tester.c:831)
   by 0x4045E1: main (test-gdbus-client.c:986)

pstglia/external-bluetooth-bluez,pstglia/external-bluetooth-bluez,silent-snowman/bluez,pkarasev3/bluez,mapfau/bluez,ComputeCycles/bluez,ComputeCycles/bluez,ComputeCycles/bluez,ComputeCycles/bluez,pkarasev3/bluez,pstglia/external-bluetooth-bluez,pkarasev3/bluez,silent-snowman/bluez,silent-snowman/bluez,mapfau/bluez,pkarasev3/bluez,mapfau/bluez,silent-snowman/bluez,mapfau/bluez,pstglia/external-bluetooth-bluez