fix: restore properly-bundled hashFiles index.js and patch GetNextMessageAsync mock

- Restore src/Misc/layoutbin/hashFiles/index.js from commit b06c585 so
  @actions/glob is bundled inline by ncc rather than externalized. The
  previous regeneration was done without running npm install first, causing
  ncc to fall back to require("@actions/glob") which is not available at
  runtime.

- Fix flaky GetNextMessageAsync mock in TestRunAsync: after Task.Delay
  resolves (either by timeout or cancellation) return null when the queue
  is empty instead of calling Dequeue() on an empty queue which would
  throw InvalidOperationException.

Agent-Logs-Url: https://github.com/actions/runner/sessions/9ceb7e98-b518-4b84-b302-29b0ed28500b

src/Test/L0/Listener/RunnerL0.cs

@@ -121,6 +121,7 @@ namespace GitHub.Runner.Common.Tests.Listener
                             {
                                 signalWorkerComplete.Release();
                                 await Task.Delay(2000, hc.RunnerShutdownToken);
+                                return null;
                             }
 
                             return messages.Dequeue();