GPAW_PLATFORM is no longer computed correctly

I'm not sure what component sets those lib build paths, whether it's something related to python itself, as I don't see any changes in the documentation of sysconfig.get_python_version() in https://docs.python.org/3.11/library/sysconfig.html. I see in relation to the python 3.10 -> 3.11 transition that in the latter case GPAW_PLATFORM is not longer computed correctly. On python I get 3.10 build/lib.linux-x86_64-3.10 vs python 3.11 build/lib.linux-x86_64-cpython-311, but this is not reflected in sysconfig.get_python_version()

docker run -it --rm --name python python:3.10.7-slim-bullseye python -c "from distutils import util, sysconfig; print(util.get_platform()+'-'+sysconfig.get_python_version())"
docker run -it --rm --name python python:3.11.0rc2-slim-bullseye python -c "from distutils import util, sysconfig; print(util.get_platform()+'-'+sysconfig.get_python_version())"

Output:

linux-x86_64-3.10  # ok, should be linux-x86_64-3.10
linux-x86_64-3.11  # wrong, should be linux-x86_64-cpython-311

I don't see any key in sysconfig.get_config_vars() that could be used instead of sysconfig.get_python_version() to accomodate this change in the lib path name.