Bump Xunit from 2.6.3 to 2.6.4 in /src

Bumps [Xunit](https://github.com/xunit/xunit) from 2.6.3 to 2.6.4.
- [Commits](xunit/xunit@2.6.3...2.6.4)

---
updated-dependencies:
- dependency-name: Xunit
  dependency-type: direct:production
  update-type: version-update:semver-patch
...

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

src/Tests/Tests.csproj

@@ -4,7 +4,7 @@
   </PropertyGroup>
   <ItemGroup>
     <PackageReference Include="FluentAssertions" Version="6.12.0" />
-    <PackageReference Include="Xunit" Version="2.6.3" />
+    <PackageReference Include="Xunit" Version="2.6.4" />
     <PackageReference Include="xunit.runner.visualstudio" Version="2.5.6" PrivateAssets="all" />
     <PackageReference Include="Microsoft.NET.Test.Sdk" Version="17.8.0" />
     <PackageReference Include="Verify.Xunit" Version="22.8.0" />