tests: Don’t run Python tests under Valgrind

The Python runtime is not amenable to Valgrind, and leak checking is a
lot less relevant in Python compared to C.

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

Helps: #487

gobject/tests/meson.build

@@ -117,7 +117,7 @@ foreach test_name : python_tests
     python,
     args: ['-B', files(test_name)],
     env: test_env,
-    suite: ['gobject'],
+    suite: ['gobject', 'no-valgrind'],
   )
 
   if installed_tests_enabled