pw-dump: sync on metadata change so that changes are displayed soon
In order to show metadata changes when monitoring, a sync must be
triggered just like it is done for other objects, to make sure that
dump_objects()
is called some time later and the changed metadata
objects are shown.
Otherwise metadata changes would never be displayed unless there was a change to a different type of object, whose event handlers do trigger a sync.
Fixes #4053 (closed)