add coverage to collectors tests

Author: MarcoRossignoli

test/coverlet.collector.tests/coverlet.collector.tests.csproj

@@ -1,4 +1,5 @@
 <Project Sdk="Microsoft.NET.Sdk">
+  <Import Project="$(RepoRoot)src\coverlet.msbuild.tasks\coverlet.msbuild.props" />
 
   <PropertyGroup>
     <TargetFramework>netcoreapp2.2</TargetFramework>
@@ -22,4 +23,5 @@
     <ProjectReference Include="$(RepoRoot)src\coverlet.collector\coverlet.collector.csproj" />
   </ItemGroup>
 
+  <Import Project="$(RepoRoot)src\coverlet.msbuild.tasks\coverlet.msbuild.targets" />
 </Project>