How to block a non-compliant open-source license before merge

Repository xlliu/e2e-license-gate has an open GPL-3.0-only finding (strong copyleft), and the overview says “License gate did not pass. Merge rejected”. The license gate decides whether a merge is allowed from the open-source licenses on dependencies. This article uses that repository to show the setup and where the result appears. Policy [System] GIT Inbound does not include License compliance, so the allowed and denied lists are empty.