ci: remove TARGET env for cygwin

Author: Berrysoft

.github/workflows/libloading.yml

@@ -81,7 +81,6 @@ jobs:
       - run: echo "INPUT(libmsys-2.0.a)" | Out-File -FilePath "C:\msys64\usr\lib\libcygwin.a"
       - run: cargo test --target x86_64-pc-cygwin -Zbuild-std
         env:
-          TARGET: x86_64-pc-windows-msvc
           CARGO_TARGET_X86_64_PC_CYGWIN_LINKER: C:\msys64\usr\bin\x86_64-pc-msys-gcc.exe
 
   bare-cross-build: