Avalonia 适配Win7

  <PropertyGroup>
    <ManagePackageVersionsCentrally>true</ManagePackageVersionsCentrally>
    <!-- 默认使用高版本（Windows 10/11） -->
    <SkiaSharpVersion>3.119.0</SkiaSharpVersion>
    <SkiaSharpWin32Version>3.119.1</SkiaSharpWin32Version>
    <!-- 如果是 Windows 7 系统，覆盖为兼容版本 -->
    <SkiaSharpVersion Condition="$([System.Environment]::OSVersion.Version.Major) == 6 AND $([System.Environment]::OSVersion.Version.Minor) == 1">3.116.0</SkiaSharpVersion>
    <SkiaSharpWin32Version Condition="$([System.Environment]::OSVersion.Version.Major) == 6 AND $([System.Environment]::OSVersion.Version.Minor) == 1">3.116.1</SkiaSharpWin32Version>
  </PropertyGroup>