Re-added a closing curly bracket in mod test_helpers = Fixing my earlier merge mess up.

Author: peter-lyons-kehl

library/alloc/src/lib.rs

@@ -285,5 +285,5 @@ pub(crate) mod test_helpers {
         let seed: [u8; 16] = seed_vec.as_slice().try_into().unwrap();
         rand::SeedableRng::from_seed(seed)
     }
-
+}