Force recycle intermediate collection in Hash#transform_keys! [Bug #17735]

* Force recycle intermediate hash

* Force recycle intermediate array too

https://github.com/ruby/ruby/pull/4329#issuecomment-808840718

hash.c

@@ -3294,7 +3294,9 @@ rb_hash_transform_keys_bang(int argc, VALUE *argv, VALUE hash)
             rb_hash_aset(new_keys, new_key, Qnil);
         }
         rb_ary_clear(pairs);
+        rb_gc_force_recycle(pairs);
         rb_hash_clear(new_keys);
+        rb_gc_force_recycle(new_keys);
     }
     return hash;
 }