ci: windows: use builtin GHC clang toolchain to build dependencies

[elopez]

Description

MSYS2 recently got its Clang updated from v18 to v19, and that caused build failures such as the following:

ghc-9.6.5.exe: loadArchive: GNU-variant filename offset 31 invalid (range [0..964]) while reading filename from `D:\a_temp\msys64\clang64\lib\libmingw32.a'

<no location info>: error:
loadArchive "D:\a\_temp\msys64\clang64\lib\libmingw32.a": failed
[29 of 29] Compiling Paths_hevm ( D:\a\hevm\hevm\dist-newstyle\build\x86_64-windows\ghc-9.6.5\hevm-0.53.0\build\autogen\Paths_hevm.hs, D:\a\hevm\hevm\dist-newstyle\build\x86_64-windows\ghc-9.6.5\hevm-0.53.0\build\Paths_hevm.o )

This PR switches the Windows build to use the toolchain shipped together with GHC to avoid the incompatibility issues.

Checklist

• tested locally
• added automated tests
• updated the docs
• updated the changelog