Bump Microsoft.NET.Test.Sdk from 17.6.0 to 18.5.1

---
updated-dependencies:
- dependency-name: Microsoft.NET.Test.Sdk
  dependency-version: 18.5.1
  dependency-type: direct:production
  update-type: version-update:semver-major
...

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

Author: dependabot[bot]

Directory.Packages.props

@@ -22,7 +22,7 @@
 
     <PackageVersion Include="MinVer" Version="6.0.0" />
 
-    <PackageVersion Include="Microsoft.NET.Test.Sdk" Version="17.6.0" />
+    <PackageVersion Include="Microsoft.NET.Test.Sdk" Version="18.5.1" />
     <PackageVersion Include="xunit" Version="2.4.2" />
     <PackageVersion Include="xunit.runner.visualstudio" Version="2.4.5" />
     <PackageVersion Include="coverlet.collector" Version="6.0.0" />