ci(github): also skip logs of broken test cases

When a test fails in the GitHub Actions CI pipeline, we mark it up using
special GitHub syntax so it stands out when looking at the run log. We
also mark up "fixed" test cases, and skip passing tests since we want to
concentrate on the failures.

The finalize_test_case_output function in
test-lib-github-workflow-markup.sh which performs this markup is however
missing a fourth case: "broken" tests, i.e. tests using
'test_expect_failure' to document a known bug. This leads to these
"broken" tests appearing along with any failed tests, potentially
confusing the reader who might not be aware that "broken" is the status
for 'test_expect_failure' tests that indeed failed, and wondering what
their commits "broke".

Also skip these "broken" tests so that only failures and fixed tests
stand out.

Signed-off-by: Philippe Blain <levraiphilippeblain@gmail.com>
Acked-by: Victoria Dye <vdye@github.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>