fix(ci): 修复 Windows 构建清理命令语法问题

- 将 rm -rf 改为 PowerShell 兼容的 Remove-Item 命令
- 解决 Windows PowerShell 不支持 bash 语法的错误

Author: EightDoor

.github/workflows/desktop-release.yml

@@ -169,8 +169,8 @@ jobs:
       - name: Clean Build Directories for Windows
         if: contains(matrix.config.goos, 'windows')
         run: |
-          rm -rf app/build
-          rm -rf app/kernel
+          Remove-Item -Recurse -Force app/build -ErrorAction SilentlyContinue
+          Remove-Item -Recurse -Force app/kernel -ErrorAction SilentlyContinue
         working-directory: ${{ github.workspace }}/repo/siyuan
 
       - name: Building Kernel