Bump Microsoft.NET.Test.Sdk from 17.2.0 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-major
...

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

Author: dependabot[bot]

Directory.Packages.props

@@ -6,7 +6,7 @@
 		<PackageVersion  Include="D2L.Services.Core.Exceptions" Version="2.0.1.15" />
 		<PackageVersion  Include="FluentAssertions" Version="6.6.0" />
 		<PackageVersion  Include="Microsoft.Extensions.Caching.Memory" Version="6.0.1" />
-		<PackageVersion  Include="Microsoft.NET.Test.Sdk" Version="17.2.0" />
+		<PackageVersion  Include="Microsoft.NET.Test.Sdk" Version="18.8.1" />
 		<PackageVersion  Include="Moq" Version="4.18.1" />
 		<PackageVersion  Include="NUnit" Version="3.14.0" />
 		<PackageVersion  Include="NUnit3TestAdapter" Version="4.5.0" />