docs: update examples using getKey

Author: SeanCassiere

docs/router/framework/react/guide/scroll-restoration.md

@@ -71,7 +71,9 @@ Falling in behind Remix's own Scroll Restoration APIs, you can also customize th
 
 The `getKey` option receives the relevant `Location` state from TanStack Router and expects you to return a string to uniquely identify the scrollable measurements for that state.
 
-The default `getKey` is `(location) => location.state.key!`, where `key` is the unique key generated for each entry in the history.
+The default `getKey` is `(location) => location.state.__TSR_key!`, where `__TSR_key` is the unique key generated for each entry in the history.
+
+> Older versions, prior to `v1.121.34`, used `state.key` as the default key, but this has been deprecated in favor of `state.__TSR_key`. For now, `location.state.key` will still be available for compatibility, but it will be removed in the next major version.
 
 ## Examples
 
@@ -95,7 +97,7 @@ const router = createRouter({
     const paths = ['/', '/chat']
     return paths.includes(location.pathname)
       ? location.pathname
-      : location.state.key!
+      : location.state.__TSR_key!
   },
 })
 ```