[vala/staging] tests: Fix "methods/extern" test with -Werror=address and gcc 5.4.0

[Rico Tzschichholz <ricotz src gnome org>]

commit 31c255dc6b2796191e19abcbc4506ae7de319013
Author: Rico Tzschichholz <ricotz ubuntu com>
Date:   Fri Jul 17 23:43:23 2020 +0200

    tests: Fix "methods/extern" test with -Werror=address and gcc 5.4.0

 tests/methods/extern.vala | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)
---
diff --git a/tests/methods/extern.vala b/tests/methods/extern.vala
index 45ee4b3f7..5681b0d27 100644
--- a/tests/methods/extern.vala
+++ b/tests/methods/extern.vala
@@ -25,7 +25,7 @@ void main () {
        assert ("foo" == Foo.strdup ("foo"));
        assert ("foo" == Bar.strdup ("foo"));
 
-       assert (some_thing != null);
-       assert (Foo.some_thing != null);
-       assert (Bar.some_thing != null);
+       assert ((void*) some_thing != null);
+       assert ((void*) Foo.some_thing != null);
+       assert ((void*) Bar.some_thing != null);
 }