macOS is proprietary software. You need a license for every copy you run, whether it's in a VM or not. The VM limit is written into the macOS EULA.

> to install, use and run up to two (2) additional copies or instances of the Apple Software, or any prior macOS or OS X operating system software or subsequent release of the Apple Software, within virtual operating system environments on each Apple-branded computer you own or control that is already running the Apple Software, for purposes of: (a) software development; (b) testing during software development; (c) using macOS Server; or (d) personal, non-commercial use.