t/helper: mark more unused argv/argc arguments

t/helper: mark more unused argv/argc arguments

This is a continuation of 126e3b3d2a (t/helper: mark unused argv/argc
arguments, 2023-03-28) to cover a few new cases:

 - test-example-tap was added since that commit

 - test-hashmap used to accept the "ignorecase" argument on the command
   line. But since most of its logic was moved to a unit-test in
   3469a23659 (t: port helper/test-hashmap.c to unit-tests/t-hashmap.c,
   2024-08-03), it now ignores its argv entirely.

Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>