Backport PR #10651: Fixed event handler in debugger session test (#10658)

Co-authored-by: Johan Mabille <johan.mabille@gmail.com>

packages/debugger/test/session.spec.ts

@@ -157,6 +157,8 @@ describe('protocol', () => {
             break;
           }
           case 'stopped':
+            const msg = event as DebugProtocol.StoppedEvent;
+            threadId = msg.body.threadId!;
             stoppedFuture.resolve();
             break;
           default: