t/t5571-prep-push-hook.sh: Add test with writing to stderr

The 2.53.0.rc0.windows release candidate had a regression where
writing to stderr from a pre-push hook would error out.

The regression was fixed in 2.53.0.rc1.windows and the test here ensures
that this stays fixed.

Signed-off-by: Thomas Braun <thomas.braun@virtuell-zuhause.de>

Author: t-b

t/t5571-pre-push-hook.sh

@@ -138,4 +138,16 @@ test_expect_success 'sigpipe does not cause pre-push hook failure' '
 	git push parent1 "refs/heads/b/*:refs/heads/b/*"
 '
 
+test_expect_success 'can write to stderr' '
+	test_hook --clobber pre-push <<-\EOF &&
+	echo foo >/dev/stderr &&
+	exit 0
+	EOF
+
+	test_commit third &&
+	echo foo >expect &&
+	git push --quiet parent1 HEAD 2>actual &&
+	test_cmp expect actual
+'
+
 test_done