Bump Microsoft.NET.Test.Sdk from 18.0.1 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

@@ -7,7 +7,7 @@
     <PackageVersion Include="DotNet.ReproducibleBuilds" Version="2.0.2" />
     <PackageVersion Include="FluentAssertions" Version="8.8.0" />
     <PackageVersion Include="ListShuffle" Version="2.1.3" />
-    <PackageVersion Include="Microsoft.NET.Test.Sdk" Version="18.0.1" />
+    <PackageVersion Include="Microsoft.NET.Test.Sdk" Version="18.8.1" />
     <PackageVersion Include="System.Net.Http" Version="4.3.4" />
     <PackageVersion Include="System.Text.RegularExpressions" Version="4.3.1" />
     <PackageVersion Include="System.Threading.Tasks.Extensions" Version="4.6.3" />