t/helper: fix leaking subrepo in nested submodule config helper

In the "submodule-nested-repo-config" helper we create a submodule
repository and print its configuration. We do not clear the repo,
causing a memory leak. Plug it.

Signed-off-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

t/helper/test-submodule-nested-repo-config.c

@@ -29,6 +29,6 @@ int cmd__submodule_nested_repo_config(int argc, const char **argv)
 	print_config_from_gitmodules(&subrepo, argv[2]);
 
 	submodule_free(the_repository);
-
+	repo_clear(&subrepo);
 	return 0;
 }