dispatch-obsolete: loosen assertion about AddDispatchOperation's channel properties
dispatch-obsolete: loosen assertion about AddDispatchOperation's channel properties

Previously, we asserted that we got the complete set of immutable
properties here, but I suspect that this was only by winning a race.
Instead, assert that we get a subset, including at least those that were
in the NewChannel signal.

freedesktop-unofficial-mirror/telepathy__telepathy-mission-control,freedesktop-unofficial-mirror/telepathy__telepathy-mission-control,freedesktop-unofficial-mirror/telepathy__telepathy-mission-control,freedesktop-unofficial-mirror/telepathy__telepathy-mission-control