Update SixLabors.ImageSharp to version 3.1.6

Updated the SixLabors.ImageSharp package in Moonglade.Setup.csproj
from version 3.1.5 to 3.1.6. This update likely includes bug fixes,
performance improvements, or new features.

src/Moonglade.Setup/Moonglade.Setup.csproj

@@ -9,7 +9,7 @@
         <ImplicitUsings>enable</ImplicitUsings>
     </PropertyGroup>
     <ItemGroup>
-      <PackageReference Include="SixLabors.ImageSharp" Version="3.1.5" />
+      <PackageReference Include="SixLabors.ImageSharp" Version="3.1.6" />
     </ItemGroup>
     <ItemGroup>
         <ProjectReference Include="..\Moonglade.Configuration\Moonglade.Configuration.csproj" />