Bump Microsoft.NET.Test.Sdk from 18.5.1 to 18.6.0

---
updated-dependencies:
- dependency-name: Microsoft.NET.Test.Sdk
  dependency-version: 18.6.0
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

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

Author: dependabot[bot]

Source/spamfilter/spamfilter.BL.Tests/spamfilter.BL.Tests.csproj

@@ -10,7 +10,7 @@
 
     <ItemGroup>
       <PackageReference Include="altcover" Version="9.0.102" />
-      <PackageReference Include="Microsoft.NET.Test.Sdk" Version="18.5.1" />
+      <PackageReference Include="Microsoft.NET.Test.Sdk" Version="18.6.0" />
       <PackageReference Include="xunit" Version="2.9.3" />
       <PackageReference Include="xunit.runner.visualstudio" Version="3.1.5">
         <IncludeAssets>runtime; build; native; contentfiles; analyzers; buildtransitive</IncludeAssets>