Bump SixLabors.ImageSharp in /lib/PuppeteerSharp.Tests

Bumps [SixLabors.ImageSharp](https://github.com/SixLabors/ImageSharp) from 1.0.4 to 2.1.9.
- [Release notes](https://github.com/SixLabors/ImageSharp/releases)
- [Commits](SixLabors/ImageSharp@v1.0.4...v2.1.9)

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

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

lib/PuppeteerSharp.Tests/PuppeteerSharp.Tests.csproj

@@ -15,7 +15,7 @@
 		  <PrivateAssets>all</PrivateAssets>
 		  <IncludeAssets>runtime; build; native; contentfiles; analyzers; buildtransitive</IncludeAssets>
 		</PackageReference>
-		<PackageReference Include="SixLabors.ImageSharp" Version="1.0.4" />
+		<PackageReference Include="SixLabors.ImageSharp" Version="2.1.9" />
 		<PackageReference Include="Microsoft.AspNetCore.Connections.Abstractions" Version="2.2.0" />
 		<PackageReference Include="Microsoft.Bcl.AsyncInterfaces" Version="6.0.0-preview.2.21154.6" />
 	</ItemGroup>