t4062: use less than 256 repetitions in regex

t4062: use less than 256 repetitions in regex

OpenBSD's regex library has a repetition limit (RE_DUP_MAX) of 255.
That's the minimum acceptable value according to POSIX.  In t4062 we use
4096 repetitions in the test "-G matches", though, causing it to fail.
Combine two repetition operators, both less than 256, to arrive at 4096
zeros instead of using a single one, to fix the test on OpenBSD.

Original-patch-by: David Coppa <dcoppa@openbsd.org>
Signed-off-by: Rene Scharfe <l.s.r@web.de>
Signed-off-by: Junio C Hamano <gitster@pobox.com>