🐛 [.github] disable Windows/MSYS2 workflows for now

[stnolting]

This PR temporarily disables the Windows-based msys2 workflows.

The latest version of the MSYS2 mingw-w64-riscv64-unknown-elf-gcc package does not work with the current NEORV32 setup:

d:/a/_temp/msys64/mingw32/bin/../lib/gcc/riscv64-unknown-elf/12.2.0/../../../../riscv64-unknown-elf/bin/ld.exe: d:/a/_temp/msys64/mingw32/bin/../lib/gcc/riscv64-unknown-elf/12.2.0/../../../../riscv64-unknown-elf/lib\libc.a(lib_a-memcpy.o): ABI is incompatible with that of the selected emulation:
  target emulation `elf64-littleriscv' does not match `elf32-littleriscv'

This package uses RISC-V GCC version 12.2. I am not sure if there is a problem with the compiler flags (-misa-spec?!) or with the package itself (compiled without rv32 support?!). However, I am analyzing this issue.