bisect run: fix the error message

bisect run: fix the error message

In d1bbbe45df8 (bisect--helper: reimplement `bisect_run` shell function
in C, 2021-09-13), we ported the `bisect run` subcommand to C, including
the part that prints out an error message when the implicit `git bisect
bad` or `git bisect good` failed.

However, the error message was supposed to print out whether the state
was "good" or "bad", but used a bogus (because non-populated) `args`
variable for it. This was fixed in [1], but as of [2] (when
`bisect--helper` was changed to the present `bisect-state') the error
message still talks about implementation details that should not
concern end users.

Fix that, and add a regression test to ensure that the intended form of
the error message.

1. 80c2e9657f2 (bisect--helper: report actual bisect_state() argument
   on error, 2022-01-18
2. f37d0bdd42d (bisect: fix output regressions in v2.30.0, 2022-11-10)

Helped-by: Elijah Newren <newren@gmail.com>
Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Signed-off-by: Ævar Arnfjörð Bjarmason <avarab@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>