canInvite was only recomputed on third party invite state events, so granting or
revoking the power to invite left the member list header button in its previous
enabled or disabled state until the list was reopened.
Recompute it on RoomStateEvent.Update as well, which also covers the space join
rule branch in canInviteTo(), matching RoomSummaryCardViewModel.
Co-authored-by: Michael Telatynski <7t3chguy@gmail.com>