Fixed a bug where the summary could become visible even if it was suppressed

Because the updating of the suppression was prohibited, some groups could loose
their suppression state when they were heads upped. This would lead to duplicate
notifications. We're now still allowing the state to be properly modified instead
but don't notify listeners anymore since that was only an internal update.

Change-Id: I6ae96ea8cfab00ef6bdb1ef047f8b77ea88e8206
Fixes: 30608517