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>

t/t4062-diff-pickaxe.sh

@@ -14,8 +14,10 @@ test_expect_success setup '
 	test_tick &&
 	git commit -m "A 4k file"
 '
+
+# OpenBSD only supports up to 255 repetitions, so repeat twice for 64*64=4096.
 test_expect_success '-G matches' '
-	git diff --name-only -G "^0{4096}$" HEAD^ >out &&
+	git diff --name-only -G "^(0{64}){64}$" HEAD^ >out &&
 	test 4096-zeroes.txt = "$(cat out)"
 '