worker: build fastchess with build=release for static linking on Windows

[maximmasiutin]

Build fastchess with build=release to ensure static linking on Windows.

Without this, the binary depends on MSYS64 UCRT DLLs, causing nanosleep64 entry point errors or Engine didn't respond to uciok failures when run outside MSYS64.

Related: Disservin/fastchess#950

[Disservin]

i don't understand this.. the environment you compile fastchess in, is also the one supposed to execute it.. there's no need for static linking

[ppigazzini]

msys2 ucrt64 builds an application that needs:

• msys2 ucrt64 dlls, for fastchess they are:

  c/msys64/ucrt64/bin/libgcc_s_seh-1.dll
  c/msys64/ucrt64/bin/libwinpthread-1.dll
  c/msys64/ucrt64/bin/libstdc++-6.dll 

• Microsoft UCRT dlls

If fastchess.exe does not find the 3 msys2 ucrt64 libraries, neither python3.exe, g++.exe, stockfish.exe should find their required libraries.