fix: remove duplicate AddGlobalInboxAttributesAsync call in async pipeline builder

The async BuildAsyncPipeline method had a duplicate call to
AddGlobalInboxAttributesAsync outside the cache-miss block, causing
static cache pollution between tests. Tests without inbox configuration
would pick up cached inbox attributes from earlier tests, then fail
with ArgumentOutOfRangeException when the handler factory couldn't
create UseInboxHandlerAsync.

The sync BuildPipeline method correctly only calls AddGlobalInboxAttributes
once inside the cache-miss block.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: holytshirt

src/Paramore.Brighter/PipelineBuilder.cs

@@ -256,9 +256,6 @@ private IHandleRequestsAsync<TRequest> BuildAsyncPipeline(RequestHandlerAsync<TR
 
             }
 
-
-            AddGlobalInboxAttributesAsync(ref preAttributes, implicitHandler);
-            
             var firstInPipeline = PushOntoAsyncPipeline(preAttributes, implicitHandler, requestContext, instanceScope, continueOnCapturedContext);
 
             if (!s_postAttributesMemento.TryGetValue(implicitHandler.Name.ToString(), out IOrderedEnumerable<RequestHandlerAttribute>? postAttributes))