bitbake: cache: appends change msg should be debug only

This quiets the odd message shown to the user every time the appends for
a given recipe change. It has no context, since the message before it was
a debug message.

Signed-off-by: Christopher Larson <chris_larson@mentor.com>
(cherry picked from commit 178db8e4016f5de86645683c159a6aa94c72547b)

Signed-off-by: Michael Brown <mw_brown@mentor.com>