use a relative dir for caching on windows

.github/workflows/windows.yml

@@ -23,8 +23,6 @@ jobs:
 
       - name: Set up Go
         uses: actions/setup-go@v6
-        with:
-          cache: false
 
       - name: Build with Flutter
         run: |

hook/build.dart

@@ -18,6 +18,7 @@ Future<void> main(List<String> args) => build(args, (input, output) async {
       break;
     case OS.windows:
       libFileName = "libgomuks.dll";
+      env = {"GOCACHE": "build/cache"};
       break;
     case OS.android:
       libFileName = "libgomuks.so";