Bump Xunit from 2.6.3 to 2.6.4 in /src (#794)

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] <[email protected]>
Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

Author: dependabot[bot]

src/Tests/Tests.csproj

@@ -6,7 +6,7 @@
     <PackageReference Include="MarkdownSnippets.MsBuild" Version="26.0.0" />
     <PackageReference Include="Microsoft.NET.Test.Sdk" Version="17.8.0" />
     <PackageReference Include="Microsoft.NETFramework.ReferenceAssemblies" Version="1.0.3" />
-    <PackageReference Include="Xunit" Version="2.6.3" />
+    <PackageReference Include="Xunit" Version="2.6.4" />
     <PackageReference Include="Verify.Nunit" Version="22.10.2" />
     <ProjectReference Include="..\TextCopy\TextCopy.csproj" />
     <PackageReference Include="ProjectDefaults" Version="1.0.108" PrivateAssets="all" />