[NetworkManager-openvpn] all: fix a bad function pointer cast

[Lubomir Rintel <lkundrak src gnome org>]

commit 5c9656be4682b3cd6bbd8c593348cc75ab66c1ad
Author: Lubomir Rintel <lkundrak v3 sk>
Date:   Fri Jun 8 11:49:59 2018 +0200

    all: fix a bad function pointer cast
    
    This makes GCC 8 unhappy, almost sad.
    
    https://gitlab.gnome.org/GNOME/NetworkManager-openvpn/merge_requests/3

 properties/tests/test-import-export.c | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)
---
diff --git a/properties/tests/test-import-export.c b/properties/tests/test-import-export.c
index 8a137aa..8e855d3 100644
--- a/properties/tests/test-import-export.c
+++ b/properties/tests/test-import-export.c
@@ -237,8 +237,7 @@ remove_secrets (NMConnection *connection)
        for (iter = keys; iter; iter = g_slist_next (iter))
                nm_setting_vpn_remove_secret (s_vpn, (const char *) iter->data);
 
-       g_slist_foreach (keys, (GFunc) g_free, NULL);
-       g_slist_free (keys);
+       g_slist_free_full (keys, g_free);
 }
 
 static void