It looks like that warning comes from a Debian-specific patch: https://salsa.debian.org/postfix-team/postfix-dev/blob/7fd2e6facc18bbe22829735fc94d6eee7e58fc0f/debian/patches/70_postfix-check.diff#L15
introduced two years ago: https://salsa.debian.org/postfix-team/postfix-dev/commit/1819dbdcd43b9c6c53f81c499101b7b59d371c4a Francois -- https://fmarier.org/