tests: Add some assertions to avoid unused variable warnings on Clang

Signed-off-by: Philip Withnall <withnall@endlessm.com>

glib/tests/autoptr.c

@@ -180,6 +180,7 @@ test_g_main_context_pusher (void)
   if (TRUE)
     {
       g_autoptr(GMainContextPusher) val = g_main_context_pusher_new (context);
+      g_assert_nonnull (val);
 
       /* Check it’s now the thread-default main context */
       g_assert_true (g_main_context_get_thread_default () == context);

gobject/tests/autoptr.c

@@ -77,6 +77,7 @@ test_autoptr (void)
 
   {
     g_autoptr (TestAutoCleanup) tac = tac_ptr;
+    g_assert_nonnull (tac);
   }
 #ifdef __GNUC__
   g_assert_null (tac_ptr);