Bump SixLabors.ImageSharp from 3.1.2 to 3.1.3 in /src/Verify.DocNet (#362)

Author: dependabot[bot]

src/Verify.DocNet/Verify.DocNet.csproj

@@ -5,7 +5,7 @@
   <ItemGroup>
     <PackageReference Include="Argon" Version="0.17.0" />
     <PackageReference Include="Docnet.Core" Version="2.6.0" />
-    <PackageReference Include="SixLabors.ImageSharp" Version="3.1.2" />
+    <PackageReference Include="SixLabors.ImageSharp" Version="3.1.3" />
     <PackageReference Include="Verify" Version="23.2.2" />
     <PackageReference Include="ProjectDefaults" Version="1.0.125" PrivateAssets="all" />
   </ItemGroup>