bugreport tests: tighten up "git bugreport -s hooks" test

Amend a test added in 788a776069b (bugreport: collect list of populated hooks, 2020-05-07) to "test_cmp" for the expected output, instead of selectively using "grep" to check for specific things we either expect or don't expect in the output. As noted in a preceding commit our .git/hooks directory already contains *.sample hooks, so we have no need to clobber the prepare-commit-msg.sample hook in particular. Instead we should assert that those *.sample hooks are not included in the output, and for good measure let's add a new "unknown-hook", to check that we only look through our own known hooks. See cfe853e66be (hook-list.h: add a generated list of hooks, like config-list.h, 2021-09-26) for how we generate that data. We're intentionally not piping the "actual" output through "sort" or similar, we'd also like to check that our reported hooks are sorted. Signed-off-by: Ævar Arnfjörð Bjarmason <avarab@gmail.com> Signed-off-by: Junio C Hamano <gitster@pobox.com>