Use act in fuzz tester to flush expired work

Expired work gets scheduled in a microtask now, so we need to use `act`
to flush it.

Author: acdlite

packages/react-reconciler/src/__tests__/ReactIncrementalTriangle-test.js

@@ -432,7 +432,9 @@ describe('ReactIncrementalTriangle', () => {
         assertConsistentTree(activeLeafIndices);
       }
       // Flush remaining work
-      Scheduler.unstable_flushAllWithoutAsserting();
+      ReactNoop.act(() => {
+        Scheduler.unstable_flushAllWithoutAsserting();
+      });
       assertConsistentTree(activeLeafIndices, expectedCounterAtEnd);
     }