glib-aux/tests: avoid valgrind leak with nmtst_add_test_func()

When only running a subset of the tests (with "-p"), then valgrind
indicates a leak. Avoid that.

  $ ./tools/run-nm-test.sh -m src/core/platform/tests/test-route-linux -v
  # no leak

  $ ./tools/run-nm-test.sh -m src/core/platform/tests/test-route-linux -v -p /route/ip4
  # many leaks:
  ==1662102== 107 (96 direct, 11 indirect) bytes in 1 blocks are definitely lost in loss record 388 of 448
  ==1662102==    at 0x4848464: calloc (vg_replace_malloc.c:1340)
  ==1662102==    by 0x4F615F0: g_malloc0 (gmem.c:163)
  ==1662102==    by 0x1621A6: _nmtst_add_test_func_full (nm-test-utils.h:918)
  ==1662102==    by 0x1623EB: _nmtstp_setup_tests (test-route.c:2179)
  ==1662102==    by 0x16E53D: main (test-common.c:2693)
  ==1662102==
  {
     <insert_a_suppression_name_here>
     Memcheck:Leak
     match-leak-kinds: definite
     fun:calloc
     fun:g_malloc0
     fun:_nmtst_add_test_func_full
     fun:_nmtstp_setup_tests
     fun:main
  }

src/libnm-glib-aux/nm-test-utils.h

@@ -957,7 +957,11 @@ _nmtst_add_test_func_full(const char      *testpath,
 
     memcpy((char *) data->testpath, testpath, testpath_len);
 
-    g_test_add_data_func_full(testpath, data, _nmtst_test_run, g_free);
+    _nmtst_testdata_track_add(data, g_free);
+    g_test_add_data_func_full(testpath,
+                              data,
+                              _nmtst_test_run,
+                              _nmtst_testdata_track_steal_and_free);
 }
 
 #define nmtst_add_test_func_full(testpath, func_test, func_setup, func_teardown, ...) \