Bump Microsoft.NET.Test.Sdk from 16.9.1 to 16.9.4 (#98)

Bumps [Microsoft.NET.Test.Sdk](https://github.com/microsoft/vstest) from 16.9.1 to 16.9.4.
- [Release notes](https://github.com/microsoft/vstest/releases)
- [Commits](microsoft/vstest@v16.9.1...v16.9.4)

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test/Library.Tests/Library.Tests.csproj

@@ -10,7 +10,7 @@
 
   <ItemGroup>
     <PackageReference Include="coverlet.msbuild" Version="3.0.3" />
-    <PackageReference Include="Microsoft.NET.Test.Sdk" Version="16.9.1" />
+    <PackageReference Include="Microsoft.NET.Test.Sdk" Version="16.9.4" />
     <PackageReference Include="xunit.runner.visualstudio" Version="2.4.3" />
     <PackageReference Include="xunit" Version="2.4.1" />
   </ItemGroup>