chore(deps): 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]

Panels.Tests/Panels.Tests.csproj

@@ -21,7 +21,7 @@
       <IncludeAssets>runtime; build; native; contentfiles; analyzers; buildtransitive</IncludeAssets>
       <PrivateAssets>all</PrivateAssets>
     </PackageReference>
-    <PackageReference Include="Microsoft.NET.Test.Sdk" Version="18.7.0" />
+    <PackageReference Include="Microsoft.NET.Test.Sdk" Version="18.8.1" />
     <PackageReference Include="Verify" Version="30.5.0-beta.1" />
     <PackageReference Include="Verify.Xunit" Version="30.4.0" />
     <PackageReference Include="xunit" Version="2.9.3" />