docs(router): fix the async resources example in the route resources guide

Only the synchronous part of a route `resources` function runs in an
injection context, so the example that created `resource()` after
`await import(...)` failed the navigation with NG0203. Capture the
injector before the `await` and pass it to the resource.

Author: MeAkib

adev/src/content/guide/routing/data-fetching-with-resources.md

@@ -91,11 +91,13 @@ The `resources` function can also be `async` and return a `Promise` if you need
 
 ```ts
 resources: async (ctx) => {
+  const injector = inject(Injector);
   const {fetchUserData} = await import('./user-api');
   return {
     user: resource({
       params: () => ctx.params()['id'],
       loader: ({params: id}) => fetchUserData(id),
+      injector,
     }),
   };
 },