Possibility of b2 invocation with explicit "cxxstd=20" argument

[noboblox]

Great action. Already saved me a lot of hassle with the yml files.
I might have a little corner case(?), where it seems I need to invoke b2 with "cxxstd=20" argument.

Is this in any way possible already or would it make sense to make it possible in your opinion?

Background:
I'm experimenting with the new boost::cobalt library, which reqiures C++20 to be build.
This library-binaries doesn't seem to be build on a standard setup, either on github actions, my local environment or by downloading the pre-build windows releases.

The only way I was able to actually build it, was to invoke b2 with an explicit "cxxstd=20" argument. After that it was available inside the boost staging area. My assumption is, this is not the default value(?).