Fix Windows build: remove pycups (Linux-only) and use Windows requirements

.github/workflows/build-windows.yml

@@ -25,8 +25,7 @@ jobs:
     - name: Install dependencies
       run: |
         python -m pip install --upgrade pip
-        pip install -r requirements_gui.txt
-        pip install pyinstaller
+        pip install -r requirements_windows.txt
     
     - name: Build executable with PyInstaller
       run: python build_exe.py