t/t6030-bisect-porcelain.sh: use test_i18ngrep

Change a i18n-specific grep in t/t6030-bisect-porcelain.sh to use
test_i18ngrep instead. This was introduced in v1.7.7.2~5^2~11 and has
been broken under GETTEXT_POISON=YesPlease since.

Signed-off-by: Ævar Arnfjörð Bjarmason <avarab@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

t/t6030-bisect-porcelain.sh

@@ -152,7 +152,7 @@ test_expect_success 'bisect start: existing ".git/BISECT_START" not modified if
 	cp .git/BISECT_START saved &&
 	test_must_fail git bisect start $HASH4 foo -- &&
 	git branch > branch.output &&
-	grep "* (no branch)" branch.output > /dev/null &&
+	test_i18ngrep "* (no branch)" branch.output > /dev/null &&
 	test_cmp saved .git/BISECT_START
 '
 test_expect_success 'bisect start: no ".git/BISECT_START" if mistaken rev' '