Make test case number unique

Signed-off-by: Johannes Sixt <j6t@kdbg.org>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

diff --git a/t/t2015-checkout-patch.sh b/t/t2016-checkout-patch.sh
similarity index 100%
rename from t/t2015-checkout-patch.sh
rename to t/t2016-checkout-patch.sh