Bump SixLabors.ImageSharp in /NAPS2.Images.ImageSharp

Bumps [SixLabors.ImageSharp](https://github.com/SixLabors/ImageSharp) from 3.1.4 to 3.1.5.
- [Release notes](https://github.com/SixLabors/ImageSharp/releases)
- [Commits](SixLabors/ImageSharp@v3.1.4...v3.1.5)

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

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

NAPS2.Images.ImageSharp/NAPS2.Images.ImageSharp.csproj

@@ -25,7 +25,7 @@
     </ItemGroup>
 
     <ItemGroup>
-      <PackageReference Include="SixLabors.ImageSharp" Version="3.1.4" />
+      <PackageReference Include="SixLabors.ImageSharp" Version="3.1.5" />
     </ItemGroup>
 
     <Import Project="..\NAPS2.Setup\targets\CommonTargets.targets" />