Bump xunit from 2.5.3 to 2.6.1 (#248)

Author: dependabot[bot]

test/Directory.Build.targets

@@ -2,7 +2,7 @@
   <ItemGroup>
     <PackageReference Include="Microsoft.TestPlatform.ObjectModel" Version="17.7.2" />
     <PackageReference Include="Microsoft.NET.Test.Sdk" Version="17.7.2" />
-    <PackageReference Include="xunit" Version="2.5.3" />
+    <PackageReference Include="xunit" Version="2.6.1" />
     <PackageReference Include="xunit.runner.visualstudio" Version="2.5.3">
       <PrivateAssets>all</PrivateAssets>
       <IncludeAssets>runtime; build; native; contentfiles; analyzers; buildtransitive</IncludeAssets>