Revert "NUnit3TestAdapter"

This reverts commit c2cfaa3.

Author: SimonCropp

src/Directory.Packages.props

@@ -21,7 +21,7 @@
     <PackageVersion Include="NUnit" Version="4.4.0" />
     <PackageVersion Include="MSTest" Version="4.0.2" />
     <PackageVersion Include="MSTest.TestFramework" Version="4.0.2" />
-    <PackageVersion Include="NUnit3TestAdapter" Version="6.0.0" />
+    <PackageVersion Include="NUnit3TestAdapter" Version="5.2.0" />
     <PackageVersion Include="Polyfill" Version="9.3.1" />
     <PackageVersion Include="ProjectDefaults" Version="1.0.163" />
     <PackageVersion Include="PublicApiGenerator" Version="11.5.4" />