chore: Bump Microsoft.NET.Test.Sdk from 18.7.0 to 18.8.1

---
updated-dependencies:
- dependency-name: Microsoft.NET.Test.Sdk
  dependency-version: 18.8.1
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

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

Author: dependabot[bot]

Directory.Packages.props

@@ -30,7 +30,7 @@
 		<PackageVersion Include="Microsoft.CodeAnalysis.CSharp.CodeRefactoring.Testing" Version="1.1.2" />
 	</ItemGroup>
 	<ItemGroup>
-		<PackageVersion Include="Microsoft.NET.Test.Sdk" Version="18.7.0" />
+		<PackageVersion Include="Microsoft.NET.Test.Sdk" Version="18.8.1" />
 		<PackageVersion Include="BenchmarkDotNet" Version="0.15.8" />
 		<PackageVersion Include="NUnit" Version="4.6.1" />
 		<PackageVersion Include="NUnit3TestAdapter" Version="6.2.0" />