Fix build

Author: glucaci

src/WorkflowCore/WorkflowCore.csproj

@@ -27,6 +27,7 @@
     <PackageReference Include="System.Threading.Thread" Version="4.3.0" />
     <PackageReference Include="System.Linq.Queryable" Version="4.3.0" />
     <PackageReference Include="OpenTelemetry.Api" Version="1.1.0" />
+    <PackageReference Include="System.Diagnostics.DiagnosticSource" Version="6.0.0" />
 	<AssemblyAttribute Include="System.Runtime.CompilerServices.InternalsVisibleTo">
 		<_Parameter1>WorkflowCore.IntegrationTests</_Parameter1>
 	</AssemblyAttribute>