Bump SixLabors.ImageSharp from 1.0.0-beta0007 to 2.1.7

Bumps [SixLabors.ImageSharp](https://github.com/SixLabors/ImageSharp) from 1.0.0-beta0007 to 2.1.7.
- [Release notes](https://github.com/SixLabors/ImageSharp/releases)
- [Commits](https://github.com/SixLabors/ImageSharp/commits/v2.1.7)

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

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

CSharp-Image-Action.csproj

@@ -7,7 +7,7 @@
   </PropertyGroup>
 
   <ItemGroup>
-    <PackageReference Include="SixLabors.ImageSharp" Version="1.0.0-beta0007" />
+    <PackageReference Include="SixLabors.ImageSharp" Version="2.1.7" />
     <PackageReference Include="Octokit" Version="0.40.0" />
     <PackageReference Include="System.Threading.Tasks.Extensions" Version="4.5.3" />
   </ItemGroup>