Bump SixLabors.ImageSharp from 1.0.1 to 2.1.11 (#1533)

---
updated-dependencies:
- dependency-name: SixLabors.ImageSharp
  dependency-version: 2.1.11
  dependency-type: direct:production
...

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test/PixelConvertTest/PixelConvertTest.csproj

@@ -10,7 +10,7 @@
   </PropertyGroup>
 
   <ItemGroup>
-    <PackageReference Include="SixLabors.ImageSharp" Version="1.0.1" />
+    <PackageReference Include="SixLabors.ImageSharp" Version="2.1.11" />
     <PackageReference Include="SIPSorceryMedia.Encoders" Version="8.0.7" />
   </ItemGroup>