Bump xunit from 2.6.3 to 2.6.4 in /src/csharp/Intel

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/csharp/Intel/Iced.UnitTests/Iced.UnitTests.csproj

@@ -15,7 +15,7 @@
     <PackageReference Include="coverlet.msbuild" Version="6.0.0" />
     <!-- NOTE: when updating this thing, make sure it hasn't gotten slower (it's happened twice now!) -->
     <PackageReference Include="Microsoft.NET.Test.Sdk" Version="17.8.0" />
-    <PackageReference Include="xunit" Version="2.6.3" />
+    <PackageReference Include="xunit" Version="2.6.4" />
     <PackageReference Include="xunit.runner.console" Version="2.6.3" />
     <PackageReference Include="xunit.runner.visualstudio" Version="2.5.5" />
   </ItemGroup>