missing include in test_connections
missing include in test_connections

Thanks brcarp.

See https://github.com/libvips/libvips/issues/1571

lovell/libvips,jcupitt/libvips,lovell/libvips,lovell/libvips,lovell/libvips,jcupitt/libvips,jcupitt/libvips,jcupitt/libvips