Bump SixLabors.ImageSharp from 3.1.5 to 3.1.6 in /src (#612)

Author: dependabot[bot]

src/Directory.Packages.props

@@ -9,7 +9,7 @@
     <PackageVersion Include="NUnit" Version="4.2.2" />
     <PackageVersion Include="NUnit3TestAdapter" Version="4.6.0" />
     <PackageVersion Include="ProjectDefaults" Version="1.0.144" />
-    <PackageVersion Include="SixLabors.ImageSharp" Version="3.1.5" />
+    <PackageVersion Include="SixLabors.ImageSharp" Version="3.1.6" />
     <PackageVersion Include="Verify" Version="28.3.2" />
     <PackageVersion Include="Verify.DiffPlex" Version="3.1.2" />
     <PackageVersion Include="Verify.Nunit" Version="28.3.1" />