Bug 1854067 - [marionette] Unsubscribe correctly from PromptListener opened event. r=webdriver-reviewers,whimboo

Differential Revision: https://phabricator.services.mozilla.com/D188710

remote/marionette/navigate.sys.mjs

@@ -415,7 +415,7 @@ navigate.waitForNavigationCompleted = async function waitForNavigationCompleted(
       "XULFrameLoaderCreated",
       onBrowsingContextChanged
     );
-    driver.promptListener?.off(onPromptOpened);
+    driver.promptListener?.off("opened", onPromptOpened);
     unloadTimer?.cancel();
 
     lazy.EventDispatcher.off("page-load", onNavigation);