test client: add a comment to not leak the callback
test client: add a comment to not leak the callback

Right now there is no free function generated and this case is not using
nor even having a destroy function.

Signed-off-by: Pekka Paalanen <0f6ae7001e34c37b02fb2c1c2573ddf8f442136a@collabora.co.uk>

waltham/waltham,waltham/waltham