Bump Microsoft.NET.Test.Sdk from 18.4.0 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]

osu.Game.Rulesets.Hishigata.Tests/osu.Game.Rulesets.Hishigata.Tests.csproj

@@ -9,7 +9,7 @@
     <GenerateProgramFile>false</GenerateProgramFile>
   </PropertyGroup>
   <ItemGroup Label="Package References">
-        <PackageReference Include="Microsoft.NET.Test.Sdk" Version="18.4.0" />
+        <PackageReference Include="Microsoft.NET.Test.Sdk" Version="18.8.1" />
         <PackageReference Include="NUnit" Version="4.5.1" />
         <PackageReference Include="NUnit3TestAdapter" Version="6.2.0" />
   </ItemGroup>