Bump SixLabors.ImageSharp from 2.1.7 to 2.1.8 in /MCGalaxy

Bumps [SixLabors.ImageSharp](https://github.com/SixLabors/ImageSharp) from 2.1.7 to 2.1.8.
- [Release notes](https://github.com/SixLabors/ImageSharp/releases)
- [Commits](SixLabors/ImageSharp@v2.1.7...v2.1.8)

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

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

MCGalaxy/MCGalaxy_dotnet.csproj

@@ -6,6 +6,6 @@
   </PropertyGroup>
   <ItemGroup>
     <PackageReference Include="MySql.Data" Version="6.7.9" />
-    <PackageReference Include="SixLabors.ImageSharp" Version="2.1.7" />
+    <PackageReference Include="SixLabors.ImageSharp" Version="2.1.8" />
   </ItemGroup>
 </Project>