doc lint: fix error-hiding regression

doc lint: fix error-hiding regression

Fix the broken "make lint-docs" (or "make check-docs" at the
top-level) target, which has been broken since my cafd9828e89 (doc
lint: lint and fix missing "GIT" end sections, 2021-04-09).

The CI for "seen" is emitting an error about a broken gitlink, but due
to there being 3x scripts chained via ";" instead of "&&" we're not
carrying forward the non-zero exit code.

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