Bump SixLabors.ImageSharp from 1.0.4 to 2.1.6

Bumps [SixLabors.ImageSharp](https://github.com/SixLabors/ImageSharp) from 1.0.4 to 2.1.6.
- [Release notes](https://github.com/SixLabors/ImageSharp/releases)
- [Commits](SixLabors/ImageSharp@v1.0.4...v2.1.6)

---
updated-dependencies:
- dependency-name: SixLabors.ImageSharp
  dependency-type: direct:production
  update-type: version-update:semver-major
...

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

TexturePlugin/TexturePlugin.csproj

@@ -28,7 +28,7 @@
 
   <ItemGroup>
     <PackageReference Include="AssetsTools.NET" Version="2.0.9" />
-    <PackageReference Include="SixLabors.ImageSharp" Version="1.0.4" />
+    <PackageReference Include="SixLabors.ImageSharp" Version="2.1.6" />
   </ItemGroup>
 
   <PropertyGroup>