Bump xunit from 2.4.1 to 2.9.3

---
updated-dependencies:
- dependency-name: xunit
  dependency-version: 2.9.3
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

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

Author: dependabot[bot]

samples/snippets/csharp/tutorials/nullable-reference-migration/start/SimpleFeedReader.Tests/SimpleFeedReader.Tests.csproj

@@ -9,7 +9,7 @@
     <PackageReference Include="Microsoft.NET.Test.Sdk" Version="17.2.0" />
     <PackageReference Include="Microsoft.AspNetCore.App"  />
     <PackageReference Include="Moq" Version="4.18.1" />
-    <PackageReference Include="xunit" Version="2.4.1" />
+    <PackageReference Include="xunit" Version="2.9.3" />
     <PackageReference Include="xunit.runner.visualstudio" Version="2.4.5" />
   </ItemGroup>