Update RouteRegistrar.php (laravel#43509)

Allow a route groups to also call the dynamic where methods described in https://laravel.com/docs/9.x/routing#parameters-regular-expression-constraints

E.g.
```php
Route::prefix('/{something}')->whereIn('something', ['foo', 'bar'])->group(function() {});
```

src/Illuminate/Routing/RouteRegistrar.php

@@ -25,6 +25,7 @@
  * @method \Illuminate\Routing\RouteRegistrar prefix(string  $prefix)
  * @method \Illuminate\Routing\RouteRegistrar scopeBindings()
  * @method \Illuminate\Routing\RouteRegistrar where(array  $where)
+ * @method \Illuminate\Routing\RouteRegistrar whereIn(array|string  $parameters, array  $values)
  * @method \Illuminate\Routing\RouteRegistrar withoutMiddleware(array|string  $middleware)
  */
 class RouteRegistrar
@@ -67,6 +68,7 @@ class RouteRegistrar
         'prefix',
         'scopeBindings',
         'where',
+        'whereIn',
         'withoutMiddleware',
     ];