chore(deps): bump xunit from 2.4.2 to 2.6.4

Bumps [xunit](https://github.com/xunit/xunit) from 2.4.2 to 2.6.4.
- [Commits](xunit/xunit@2.4.2...2.6.4)

---
updated-dependencies:
- dependency-name: xunit
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

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

Directory.Packages.props

@@ -8,7 +8,7 @@
     <PackageVersion Include="Newtonsoft.Json" Version="13.0.3" />
     <PackageVersion Include="Portable.BouncyCastle" Version="1.9.0" />
     <PackageVersion Include="Websocket.Client" Version="4.6.1" />
-    <PackageVersion Include="xunit" Version="2.4.2" />
+    <PackageVersion Include="xunit" Version="2.6.4" />
     <PackageVersion Include="Microsoft.NET.Test.Sdk" Version="17.6.3" />
     <PackageVersion Include="xunit.runner.visualstudio" Version="2.5.0" />
     <PackageVersion Include="coverlet.collector" Version="3.1.0" />