According to https://blogs.msdn.microsoft.com/commandline/2017/12/22/share-environment-vars-between-wsl-and-windows/, when setting WSLENV, one can append each variable with flags that configure how the variable is shared. This includes the specifier /u which restricts the environment variable flow from Windows to WSL (which I think makes sense for this use case). Adding such a modifier causes the WSLENV variable check to fail.

Versions: tested on wslgit master on Windows 10 build 17134.345.