tests: fix warnings on tmdb missing configuration
tests: fix warnings on tmdb missing configuration

 warning: ISO C90 forbids mixed declarations and code [-Wdeclaration-after-statement]
 GrlSource *source = test_get_source();
 ^~~~~~~~~

https://bugzilla.gnome.org/show_bug.cgi?id=768557

grilofw/grilo-plugins,GNOME/grilo-plugins,grilofw/grilo-plugins,jasuarez/grilo-plugins,jasuarez/grilo-plugins,GNOME/grilo-plugins