Fix VPN view model memory leak (#2570)

Task/Issue URL: https://app.asana.com/0/414235014887631/1206803287661273/f
Tech Design URL:
CC: @graeme

Description:

This PR fixes a view model memory leak in the VPN code.

DuckDuckGo/NetworkProtectionStatusViewModel.swift

@@ -37,7 +37,6 @@ final class NetworkProtectionStatusViewModel: ObservableObject {
     private let serverInfoObserver: ConnectionServerInfoObserver
     private let errorObserver: ConnectionErrorObserver
     private var cancellables: Set<AnyCancellable> = []
-    private var delayedToggleReenableCancellable: Cancellable?
 
     // MARK: Error
 
@@ -158,12 +157,11 @@ final class NetworkProtectionStatusViewModel: ObservableObject {
         // Each event cancels the previous delayed publisher
         $shouldDisableToggle
             .filter { $0 }
-            .map {
-                Just(!$0)
-                    .delay(for: 2.0, scheduler: DispatchQueue.main)
-                    .assign(to: \.shouldDisableToggle, onWeaklyHeld: self)
+            .map { _ -> AnyPublisher<Bool, Never> in
+                Just(false).delay(for: 2.0, scheduler: DispatchQueue.main).eraseToAnyPublisher()
             }
-            .assign(to: \.delayedToggleReenableCancellable, onWeaklyHeld: self)
+            .switchToLatest()
+            .assign(to: \.shouldDisableToggle, onWeaklyHeld: self)
             .store(in: &cancellables)
     }