macos: setup the standard sparkle driver for no-window scenario

If there are no windows, we use the standard sparkle driver to drive
the standard window-based update UI.

macos/Sources/Features/Update/UpdateController.swift

@@ -18,7 +18,9 @@ class UpdateController {
     /// Initialize a new update controller.
     init() {
         let hostBundle = Bundle.main
-        self.userDriver = UpdateDriver(viewModel: .init())
+        self.userDriver = UpdateDriver(
+            viewModel: .init(),
+            hostBundle: hostBundle)
         self.updater = SPUUpdater(
             hostBundle: hostBundle,
             applicationBundle: hostBundle,

macos/Sources/Features/Update/UpdateDriver.swift

@@ -4,9 +4,11 @@ import Sparkle
 /// Implement the SPUUserDriver to modify our UpdateViewModel for custom presentation.
 class UpdateDriver: NSObject, SPUUserDriver {
     let viewModel: UpdateViewModel
+    let standard: SPUStandardUserDriver
     
-    init(viewModel: UpdateViewModel) {
+    init(viewModel: UpdateViewModel, hostBundle: Bundle) {
         self.viewModel = viewModel
+        self.standard = SPUStandardUserDriver(hostBundle: hostBundle, delegate: nil)
         super.init()
     }