docs: update stale links in README (#23262)

Author: marktnoonan

npm/react/cypress/component/advanced/react-router-v6/README.md

@@ -2,7 +2,7 @@
 
 We are testing the navigation in the [app.jsx](app.jsx) when it is surrounded by a React Router from [react-router-dom](https://github.com/ReactTraining/react-router#readme)
 
-- [spec.js](spec.js) uses `BrowserRouter`
-- [in-memory-spec.js](in-memory-spec.js) uses `MemoryRouter`
+- [spec.cy.jsx](spec.cy.jsx) uses `BrowserRouter`
+- [in-memory.cy.jsx](in-memory.cy.jsx) uses `MemoryRouter`
 
 ![In memory router spec](images/in-memory.gif)