ICU-682 Stopped sending out of channel mention warnings for system messages (#8426)

app/notification.go

@@ -89,7 +89,7 @@ func (a *App) SendNotifications(post *model.Post, team *model.Team, channel *mod
 			delete(mentionedUserIds, post.UserId)
 		}
 
-		if len(m.OtherPotentialMentions) > 0 {
+		if len(m.OtherPotentialMentions) > 0 && !post.IsSystemMessage() {
 			if result := <-a.Srv.Store.User().GetProfilesByUsernames(m.OtherPotentialMentions, team.Id); result.Err == nil {
 				outOfChannelMentions := result.Data.([]*model.User)
 				if channel.Type != model.CHANNEL_GROUP {