Bump Microsoft.NET.Test.Sdk from 15.8.0 to 15.9.0

Bumps [Microsoft.NET.Test.Sdk](https://github.com/microsoft/vstest) from 15.8.0 to 15.9.0.
- [Release notes](https://github.com/microsoft/vstest/releases)
- [Commits](microsoft/vstest@v15.8.0...v15.9.0)

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

Author: dependabot-support

Patros.AuthenticatedHttpClient.Basic.Tests/Patros.AuthenticatedHttpClient.Basic.Tests.csproj

@@ -7,7 +7,7 @@
   </PropertyGroup>
 
   <ItemGroup>
-    <PackageReference Include="Microsoft.NET.Test.Sdk" Version="15.8.0" />
+    <PackageReference Include="Microsoft.NET.Test.Sdk" Version="15.9.0" />
     <PackageReference Include="xunit" Version="2.3.1" />
     <PackageReference Include="xunit.runner.visualstudio" Version="2.3.1" />
   </ItemGroup>