alloc: fix memory leak in tests.

ccan/alloc/test/run.c

@@ -160,6 +160,8 @@ static void test(unsigned int pool_size)
 	ok1(alloc_size(mem, pool_size, p[0]) < pool_size);
 	alloc_free(mem, pool_size, p[0]);
 	ok1(alloc_check(mem, pool_size));
+
+	free(mem);
 }
 
 int main(int argc, char *argv[])