Change the "run-command" test helper to "return" instead of calling
"exit", see 338abb0f04 (builtins + test helpers: use return instead
of exit() in cmd_*, 2021-06-08)
Because we'd previously gotten past the SANITIZE=leak check by using
exit() here we need to move to "goto cleanup" pattern.
Signed-off-by: Ævar Arnfjörð Bjarmason <avarab@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>