hook tests: turn exit code assertions into a loop

hook tests: turn exit code assertions into a loop

Amend a test added in 96e7225b310 (hook: add 'run' subcommand,
2021-12-22) to use a for-loop instead of a copy/pasting the same test
for the four exit codes we test.

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