MM-54778 Fix mark as unread on GMs (#24880)

* Fix mark as unread on GMs

* Don't count own messages in gms when marking as unread

* Change argument name

* Rename userId

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Co-authored-by: Mattermost Build <build@mattermost.com>

server/channels/store/store.go

@@ -248,8 +248,8 @@ type ChannelStore interface {
 	PermanentDeleteMembersByChannel(channelID string) error
 	UpdateLastViewedAt(channelIds []string, userID string) (map[string]int64, error)
 	UpdateLastViewedAtPost(unreadPost *model.Post, userID string, mentionCount, mentionCountRoot, urgentMentionCount int, setUnreadCountRoot bool) (*model.ChannelUnreadAt, error)
-	CountPostsAfter(channelID string, timestamp int64, userID string) (int, int, error)
-	CountUrgentPostsAfter(channelID string, timestamp int64, userID string) (int, error)
+	CountPostsAfter(channelID string, timestamp int64, excludedUserID string) (int, int, error)
+	CountUrgentPostsAfter(channelID string, timestamp int64, excludedUserID string) (int, error)
 	IncrementMentionCount(channelID string, userIDs []string, isRoot, isUrgent bool) error
 	AnalyticsTypeCount(teamID string, channelType model.ChannelType) (int64, error)
 	GetMembersForUser(teamID string, userID string) (model.ChannelMembers, error)