Merge branch 'ps/check-docs-fix'

"make check-docs" noticed problems and reported to its output but
failed to signal its findings with its exit status, which has been
corrected.

* ps/check-docs-fix:
  ci/test-documentation: work around SyntaxWarning in Python 3.12
  gitlab-ci: add job to run `make check-docs`
  Documentation/lint-manpages: bubble up errors
  Makefile: extract script to lint missing/extraneous manpages

diff --cc Makefile
Simple merge