The previous idempotency checks only tested for one binary
(makemkvcon in debian, makemkv in pop_os), so a partial install
could cause a full rebuild on the next run.

Check for both makemkv and makemkvcon; skip the build only if
both are present. Also update pop_os version from 1.17.6 to
1.18.3 to match the current release.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>