Bump xunit from 2.6.3 to 2.6.4

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>

tests/Microsoft.Graph.DotnetCore.Test/Microsoft.Graph.DotnetCore.Test.csproj

@@ -18,7 +18,7 @@
   <ItemGroup>
     <PackageReference Include="Microsoft.NET.Test.Sdk" Version="17.8.0" />
     <PackageReference Include="Moq" Version="4.20.70" />
-    <PackageReference Include="xunit" Version="2.6.3" />
+    <PackageReference Include="xunit" Version="2.6.4" />
     <PackageReference Include="xunit.runner.visualstudio" Version="2.5.5">
       <PrivateAssets>all</PrivateAssets>
       <IncludeAssets>runtime; build; native; contentfiles; analyzers; buildtransitive</IncludeAssets>