For anyone curious (as I was) the basic difference is that WSL1 implemented the Linux syscall table directly whereas WSL2 actually runs Linux on top of some virtual drivers (hypervisor).
While new contributions to Forgejo will by under the GPL, old contributions coming from Gitea will still be under MIT. The original Gitea code can be sub licensed to GPL but they must still keep the MIT license around.
Presumably it quite a bit of work to track everything as either MIT + GPL or just GPL. If someone made changes to a file only containing MIT licensed code could they not still claim their contributions as MIT license to the project? Forgejo could of course decline the contribution or sub-license it as GPL but wouldn't it be possible?