Bump SixLabors.ImageSharp in /samples/ComputeSharp.Benchmark

Bumps [SixLabors.ImageSharp](https://github.com/SixLabors/ImageSharp) from 3.1.2 to 3.1.3.
- [Release notes](https://github.com/SixLabors/ImageSharp/releases)
- [Commits](SixLabors/ImageSharp@v3.1.2...v3.1.3)

---
updated-dependencies:
- dependency-name: SixLabors.ImageSharp
  dependency-type: direct:production
...

Signed-off-by: dependabot[bot] <support@github.com>

samples/ComputeSharp.Benchmark/ComputeSharp.Benchmark.csproj

@@ -20,7 +20,7 @@
   <ItemGroup>
     <PackageReference Include="BenchmarkDotNet" Version="0.13.12" />
     <PackageReference Include="CommunityToolkit.Diagnostics" Version="8.2.2" />
-    <PackageReference Include="SixLabors.ImageSharp" Version="3.1.2" />
+    <PackageReference Include="SixLabors.ImageSharp" Version="3.1.3" />
   </ItemGroup>
 
   <ItemGroup>