Bump the tests group with 1 update

Bumps Microsoft.NET.Test.Sdk from 18.3.0 to 18.4.0

---
updated-dependencies:
- dependency-name: Microsoft.NET.Test.Sdk
  dependency-version: 18.4.0
  dependency-type: direct:production
  update-type: version-update:semver-minor
  dependency-group: tests
...

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

Author: dependabot[bot]

src/xAI.Tests/xAI.Tests.csproj

@@ -16,7 +16,7 @@
     <PackageReference Include="ThisAssembly.Git" Version="2.1.2" PrivateAssets="all" />
     <PackageReference Include="xunit" Version="2.9.3" />
     <PackageReference Include="xunit.runner.visualstudio" Version="3.1.5" PrivateAssets="all" />
-    <PackageReference Include="Microsoft.NET.Test.Sdk" Version="18.3.0" />
+    <PackageReference Include="Microsoft.NET.Test.Sdk" Version="18.4.0" />
 
     <PackageReference Include="Microsoft.Extensions.Configuration" Version="10.0.5" />
     <PackageReference Include="Microsoft.Extensions.Configuration.EnvironmentVariables" Version="10.0.5" />