Plug a mem leak in the gdbus-peer test

Plug a mem leak in the gdbus-peer test

==6793== 32 (24 direct, 8 indirect) bytes in 1 blocks are definitely lost in loss record 779 of 1,423
==6793==    at 0x4005BDC: malloc (vg_replace_malloc.c:195)
==6793==    by 0x4057094: g_malloc (gmem.c:134)
==6793==    by 0x406F2D6: g_slice_alloc (gslice.c:836)
==6793==    by 0x406F31B: g_slice_alloc0 (gslice.c:848)
==6793==    by 0x413D5BB: g_type_create_instance (gtype.c:1867)
==6793==    by 0x412372A: g_object_constructor (gobject.c:1482)
==6793==    by 0x4122E1D: g_object_newv (gobject.c:1266)
==6793==    by 0x4122B93: g_object_new (gobject.c:1178)
==6793==    by 0x41DB4F9: g_unix_fd_list_new (gunixfdlist.c:159)
==6793==    by 0x804AADD: test_interface_method_call (gdbus-peer.c:172)

Bug #628331.