chore(consts): add missing as const to ACTOR_PERMISSION_LEVEL (#578)

Makes the `ACTOR_PERMISSION_LEVEL` a constant. So its options are not
considered as any string.

Author: stepskop

packages/consts/src/consts.ts

@@ -703,6 +703,6 @@ export const ACTOR_PERMISSION_LEVEL = {
      * For details refer to the Apify documentation.
      */
     LIMITED_PERMISSIONS: 'LIMITED_PERMISSIONS',
-};
+} as const;
 
 export type ACTOR_PERMISSION_LEVEL = ValueOf<typeof ACTOR_PERMISSION_LEVEL>;