Bump Microsoft.NET.Test.Sdk from 17.8.0 to 17.9.0 in /SteamKit2

Bumps [Microsoft.NET.Test.Sdk](https://github.com/microsoft/vstest) from 17.8.0 to 17.9.0.
- [Release notes](https://github.com/microsoft/vstest/releases)
- [Changelog](https://github.com/microsoft/vstest/blob/main/docs/releases.md)
- [Commits](microsoft/vstest@v17.8.0...v17.9.0)

---
updated-dependencies:
- dependency-name: Microsoft.NET.Test.Sdk
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

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

SteamKit2/Tests/Tests.csproj

@@ -11,7 +11,7 @@
 
   <ItemGroup>
     <PackageReference Include="Microsoft.AspNet.WebApi.Client" Version="6.0.0" />
-    <PackageReference Include="Microsoft.NET.Test.Sdk" Version="17.8.0" />
+    <PackageReference Include="Microsoft.NET.Test.Sdk" Version="17.9.0" />
     <PackageReference Include="xunit" Version="2.6.1" />
     <PackageReference Include="xunit.runner.visualstudio" Version="2.5.3">
       <PrivateAssets>all</PrivateAssets>