Fix retain cycle in timestamp updating code

The timestamp update work item shouldn't retain a reference to the cell.
It can be unowned because when the cell is deinit'd, the work item will
be cancelled.

Tusker/Views/Notifications/ActionNotificationGroupTableViewCell.swift

@@ -27,6 +27,10 @@ class ActionNotificationGroupTableViewCell: UITableViewCell {
     var authorAvatarURL: URL?
     var updateTimestampWorkItem: DispatchWorkItem?
     
+    deinit {
+        updateTimestampWorkItem?.cancel()
+    }
+    
     override func awakeFromNib() {
         super.awakeFromNib()
         
@@ -110,7 +114,9 @@ class ActionNotificationGroupTableViewCell: UITableViewCell {
             delay = nil
         }
         if let delay = delay {
-            updateTimestampWorkItem = DispatchWorkItem(block: self.updateTimestamp)
+            updateTimestampWorkItem = DispatchWorkItem { [unowned self] in
+                self.updateTimestamp()
+            }
             DispatchQueue.main.asyncAfter(deadline: .now() + delay, execute: updateTimestampWorkItem!)
         } else {
             updateTimestampWorkItem = nil

Tusker/Views/Notifications/FollowNotificationGroupTableViewCell.swift

@@ -22,6 +22,10 @@ class FollowNotificationGroupTableViewCell: UITableViewCell {
     
     var updateTimestampWorkItem: DispatchWorkItem?
     
+    deinit {
+        updateTimestampWorkItem?.cancel()
+    }
+    
     override func awakeFromNib() {
         super.awakeFromNib()
         
@@ -98,7 +102,7 @@ class FollowNotificationGroupTableViewCell: UITableViewCell {
             delay = nil
         }
         if let delay = delay {
-            updateTimestampWorkItem = DispatchWorkItem {
+            updateTimestampWorkItem = DispatchWorkItem { [unowned self] in
                 self.updateTimestamp()
             }
             DispatchQueue.main.asyncAfter(deadline: .now() + delay, execute: updateTimestampWorkItem!)

Tusker/Views/Notifications/FollowRequestNotificationTableViewCell.swift

@@ -27,6 +27,10 @@ class FollowRequestNotificationTableViewCell: UITableViewCell {
     
     var updateTimestampWorkItem: DispatchWorkItem?
     
+    deinit {
+        updateTimestampWorkItem?.cancel()
+    }
+    
     override func awakeFromNib() {
         super.awakeFromNib()
         
@@ -72,7 +76,9 @@ class FollowRequestNotificationTableViewCell: UITableViewCell {
             delay = nil
         }
         if let delay = delay {
-            updateTimestampWorkItem = DispatchWorkItem(block: self.updateTimestamp)
+            updateTimestampWorkItem = DispatchWorkItem { [unowned self] in
+                self.updateTimestamp()
+            }
             DispatchQueue.main.asyncAfter(deadline: .now() + delay, execute: updateTimestampWorkItem!)
         } else {
             updateTimestampWorkItem = nil

Tusker/Views/Status/TimelineStatusTableViewCell.swift

@@ -34,6 +34,7 @@ class TimelineStatusTableViewCell: BaseStatusTableViewCell {
 
     deinit {
         rebloggerAccountUpdater?.cancel()
+        updateTimestampWorkItem?.cancel()
     }
     
     override func awakeFromNib() {
@@ -109,7 +110,7 @@ class TimelineStatusTableViewCell: BaseStatusTableViewCell {
             delay = nil
         }
         if let delay = delay {
-            updateTimestampWorkItem = DispatchWorkItem {
+            updateTimestampWorkItem = DispatchWorkItem { [unowned self] in
                 self.updateTimestamp()
             }
             DispatchQueue.main.asyncAfter(deadline: .now() + delay, execute: updateTimestampWorkItem!)