Package: lintian Version: 2.5.94 Severity: minor Control: tags -1 patchautopkgtest recently (5.4) added two new Restrictions, flaky and skippable. Lintian does not know about these and hence reports unknown-runtime-tests-restriction.
This can probably be fixed by adding them to the list at https://salsa.debian.org/lintian/lintian/blob/master/checks/testsuite.pm#L48 but I haven't actually tried this.