Fix docker build
* docker/build-gpg4win-docker-image.sh: Use new system. * docker/gpg4win-bullseye/Dockerfile, docker/gpg4win-bookworm/Dockerfile: Renamed. Use bookworm now. * docker/run-gpg4win-build.sh: Use bookworm.
Using the mingw / gcc toolchain from debian stable is
still the reference platform for building Gpg4win.