t2402: use ref-store test helper to create broken symlink

Signed-off-by: Han-Wen Nienhuys <hanwen@google.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

t/t2402-worktree-list.sh

@@ -230,7 +230,7 @@ test_expect_success 'broken main worktree still at the top' '
 		EOF
 		cd linked &&
 		echo "worktree $(pwd)" >expected &&
-		echo "ref: .broken" >../.git/HEAD &&
+		(cd ../ && test-tool ref-store main create-symref HEAD .broken ) &&
 		git worktree list --porcelain >out &&
 		head -n 3 out >actual &&
 		test_cmp ../expected actual &&