Update dependency Microsoft.NET.Test.Sdk to 18.8.1 (#5600)

Co-authored-by: dependencyupdates[bot] <218638057+dependencyupdates[bot]@users.noreply.github.com>

Author: dependencyupdates[bot]

src/Directory.Packages.props

@@ -30,7 +30,7 @@
     <PackageVersion Include="Microsoft.Extensions.TimeProvider.Testing" Version="10.7.0" />
     <PackageVersion Include="Microsoft.IdentityModel.Protocols.OpenIdConnect" Version="8.19.1" />
     <PackageVersion Include="Microsoft.IdentityModel.Tokens" Version="8.19.1" />
-    <PackageVersion Include="Microsoft.NET.Test.Sdk" Version="18.8.0" />
+    <PackageVersion Include="Microsoft.NET.Test.Sdk" Version="18.8.1" />
     <PackageVersion Include="Microsoft-WindowsAPICodePack-Shell" Version="1.1.5" />
     <PackageVersion Include="Mindscape.Raygun4Net.NetCore" Version="11.2.5" />
     <PackageVersion Include="NLog.Extensions.Logging" Version="6.1.3" />