One important additional note to the following:
This check has been added to the “master” branch only (in Have greenbone-nvt-sync not run as root by janowagner · Pull Request #323 · greenbone/openvas-scanner · GitHub) which means you’re currently trying to use a development version of GVM.
Please note that the “master” branch is where all development is happening. This branch might show unexpected behavior or could even break at any time.
If you don’t want to contribute to the development of GVM and want to have the best experience with GVM it is strongly suggested to stay with the official announced source code releases in About the Greenbone Community Edition category - Greenbone Community Edition - Greenbone Community Forum.