Fix compiler issue for Xcode 16

Author: staskus

WordPressAuthenticator/Email Client Picker/URLHandler.swift

@@ -2,10 +2,18 @@
 public protocol URLHandler {
     /// checks if the specified URL can be opened
     func canOpenURL(_ url: URL) -> Bool
+
+#if compiler(>=6)
+    /// opens the specified URL
+    func open(_ url: URL,
+              options: [UIApplication.OpenExternalURLOptionsKey: Any],
+              completionHandler completion: (@MainActor @Sendable (Bool) -> Void)?)
+#else
     /// opens the specified URL
     func open(_ url: URL,
               options: [UIApplication.OpenExternalURLOptionsKey: Any],
               completionHandler completion: ((Bool) -> Void)?)
+#endif
 }
 
 /// conforms UIApplication to URLHandler to allow dependency injection