Fix leak in dualstack_socket_test
diff --git a/test/core/util/port_posix.c b/test/core/util/port_posix.c
index f139601..265e0ac 100644
--- a/test/core/util/port_posix.c
+++ b/test/core/util/port_posix.c
@@ -89,6 +89,7 @@
       grpc_free_port_using_server(env, port);
     }
   }
+  gpr_free(env);
   return found;
 }