Move glib and gtk includes out of extern C for tests.

Needed to compile with glib 2.67 and later.

libgnucash/backend/dbi/test/test-backend-dbi.cpp

@@ -19,11 +19,11 @@
  * 51 Franklin Street, Fifth Floor    Fax:    +1-617-542-2652       *
  * Boston, MA  02110-1301,  USA       gnu@gnu.org                   *
 \********************************************************************/
+#include <glib.h>
 
 extern "C"
 {
 #include <config.h>
-#include <glib.h>
 #include "qof.h"
 #include "cashobjects.h"
 }