chore: Update dependency SixLabors.ImageSharp to v2.1.6

Author: renovate[bot]

src/Spectre.Console.ImageSharp/Spectre.Console.ImageSharp.csproj

@@ -13,7 +13,7 @@
   </ItemGroup>
 
   <ItemGroup>
-    <PackageReference Include="SixLabors.ImageSharp" Version="2.1.3" />
+    <PackageReference Include="SixLabors.ImageSharp" Version="2.1.6" />
   </ItemGroup>
 
   <ItemGroup>