MM-34871 CRT: Participants of thread include non-replying followers (and past followers) (#17447)

Co-authored-by: Mattermod <mattermod@users.noreply.github.com>

app/notification.go

@@ -185,7 +185,7 @@ func (a *App) SendNotifications(post *model.Post, team *model.Team, channel *mod
 			go func(userID string) {
 				defer close(mac)
 				_, incrementMentions := mentions.Mentions[userID]
-				_, err := a.Srv().Store.Thread().MaintainMembership(userID, post.RootId, true, incrementMentions, *a.Config().ServiceSettings.ThreadAutoFollow, userID == post.UserId)
+				_, err := a.Srv().Store.Thread().MaintainMembership(userID, post.RootId, true, incrementMentions, *a.Config().ServiceSettings.ThreadAutoFollow, userID == post.UserId, userID == post.UserId)
 				if err != nil {
 					mac <- model.NewAppError("SendNotifications", "app.channel.autofollow.app_error", nil, err.Error(), http.StatusInternalServerError)
 					return