Exclude the metrics-only path from coverage.

Author: tillig

src/Autofac/Core/Resolving/Pipeline/ResolvePipelineBuilder.cs

@@ -158,6 +158,7 @@ private static ResolvePipeline BuildPipeline(MiddlewareDeclaration? lastDecl)
         return new ResolvePipeline(currentInvoke);
     }
 
+    [ExcludeFromCodeCoverage]
     private static Action<ResolveRequestContext> BuildMetricsMiddlewareChain(Action<ResolveRequestContext> next, IResolveMiddleware stage)
     {
         var stagePhase = stage.Phase;