Bump SixLabors.ImageSharp from 3.1.2 to 3.1.5 in /src/Pfim.ImageSharp

Bumps [SixLabors.ImageSharp](https://github.com/SixLabors/ImageSharp) from 3.1.2 to 3.1.5.
- [Release notes](https://github.com/SixLabors/ImageSharp/releases)
- [Commits](SixLabors/ImageSharp@v3.1.2...v3.1.5)

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

Signed-off-by: dependabot[bot] <[email protected]>

Author: dependabot[bot]

src/Pfim.ImageSharp/Pfim.ImageSharp.csproj

@@ -6,7 +6,7 @@
   </PropertyGroup>
 
   <ItemGroup>
-    <PackageReference Include="SixLabors.ImageSharp" Version="3.1.2" />
+    <PackageReference Include="SixLabors.ImageSharp" Version="3.1.5" />
   </ItemGroup>
 
   <ItemGroup>