Fix GVariant memory leaks in session test code

Fix GVariant memory leaks in session test code

==187759== 88 (40 direct, 48 indirect) bytes in 1 blocks are definitely lost in loss record 2,262 of 3,218
==187759==    at 0x4C2EBAB: malloc (vg_replace_malloc.c:299)
==187759==    by 0x563C435: g_malloc (in /usr/lib64/libglib-2.0.so.0.5600.3)
==187759==    by 0x5654056: g_slice_alloc (in /usr/lib64/libglib-2.0.so.0.5600.3)
==187759==    by 0x5673630: g_variant_new_from_bytes (in /usr/lib64/libglib-2.0.so.0.5600.3)
==187759==    by 0x566C5E6: ??? (in /usr/lib64/libglib-2.0.so.0.5600.3)
==187759==    by 0x566C7D2: g_variant_new_uint64 (in /usr/lib64/libglib-2.0.so.0.5600.3)
==187759==    by 0x403D41: conf_check_fail.constprop.6 (session.c:152)
==187759==    by 0x403E06: test_session_metadata_set_bogus (session.c:215)
==187759==    by 0x53E51D5: srunner_run_tagged (in /usr/lib64/libcheck.so.0.0.0)
==187759==    by 0x401237: main (main.c:51)