Sync Weekly Roundup and notifications switch state (#19615)

This fixes a bug where the notifications switch could be off but Weekly Roundup was still showing up in the app's UI.
#19590 hid Weekly Roundup when the switch was off. I noticed that toggling the switch wouldn't always toggle Weekly Roundup's visibility. I would need to close and re-open the Notifications Settings screen for the switch's state to take effect.

Author: Paul Von Schrottky

WordPress/Classes/Models/Notifications/NotificationSettings.swift

@@ -139,15 +139,15 @@ open class NotificationSettings {
     }
 
     // MARK: - Private Properties
-    fileprivate let blogPreferenceKeys: [String] = {
+    fileprivate var blogPreferenceKeys: [String] {
         var keys = [Keys.commentAdded, Keys.commentLiked, Keys.postLiked, Keys.follower, Keys.achievement, Keys.mention]
 
         if Feature.enabled(.weeklyRoundup) {
             keys.append(Keys.weeklyRoundup)
         }
 
         return keys
-    }()
+    }
     fileprivate let blogEmailPreferenceKeys = [Keys.commentAdded, Keys.commentLiked, Keys.postLiked, Keys.follower, Keys.mention]
     fileprivate let otherPreferenceKeys     = [Keys.commentLiked, Keys.commentReplied]
     fileprivate let wpcomPreferenceKeys     = [Keys.marketing, Keys.research, Keys.community]