Update SixLabors.ImageSharp version

Author: first-ironsoftware

IronSoftware.Drawing/IronSoftware.Drawing.Common/IronSoftware.Drawing.Common.csproj

@@ -35,8 +35,8 @@
 	<Choose>
 		<When Condition="'$(TargetFramework)' == 'net60'">
 			<ItemGroup>
-				<PackageReference Include="SixLabors.ImageSharp" Version="3.1.7" />
-				<PackageReference Include="SixLabors.ImageSharp.Drawing" Version="2.1.5" />
+				<PackageReference Include="SixLabors.ImageSharp" Version="3.1.8" />
+				<PackageReference Include="SixLabors.ImageSharp.Drawing" Version="2.1.6" />
 			</ItemGroup>
 		</When>
 		<Otherwise>