Bump the dotnet group

Bumps the dotnet group in /samples/snippets/core/testing/unit-testing-using-dotnet-test/csharp with 2 updates: xunit and xunit.runner.visualstudio.


Updates `xunit` from 2.8.1 to 2.9.0

Updates `xunit.runner.visualstudio` from 2.8.1 to 2.8.2

---
updated-dependencies:
- dependency-name: xunit
  dependency-type: direct:production
  update-type: version-update:semver-minor
  dependency-group: dotnet
- dependency-name: xunit.runner.visualstudio
  dependency-type: direct:production
  update-type: version-update:semver-patch
  dependency-group: dotnet
...

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

samples/snippets/core/testing/unit-testing-using-dotnet-test/csharp/PrimeService.Tests/PrimeService.Tests.csproj

@@ -8,8 +8,8 @@
 
   <ItemGroup>
     <PackageReference Include="Microsoft.NET.Test.Sdk" Version="17.10.0" />
-    <PackageReference Include="xunit" Version="2.8.1" />
-    <PackageReference Include="xunit.runner.visualstudio" Version="2.8.1" />
+    <PackageReference Include="xunit" Version="2.9.0" />
+    <PackageReference Include="xunit.runner.visualstudio" Version="2.8.2" />
   </ItemGroup>
 
   <ItemGroup>