test(session): de-flake SessionProvider normal-load test

flush() only drained microtasks, so the query->render update occasionally
lost the race and ctx.data was still null after the flush budget. Yield one
macrotask tick per flush so React Query's notifyManager and deferred renders
settle deterministically. Verified across repeated local runs.

Author: waleedlatif1

apps/sim/app/_shell/providers/session-provider.test.tsx

@@ -107,12 +107,18 @@ function renderProvider(): Harness {
   }
 }
 
-/** Flush pending microtasks inside an act() boundary. */
+/**
+ * Flush pending work inside an act() boundary. Drains the microtask queue and
+ * then yields one macrotask tick, so React Query's notifyManager (which can
+ * schedule observer notifications on a timer) and any deferred renders settle
+ * deterministically — microtask-only flushing raced the query→render update.
+ */
 async function flush() {
   await act(async () => {
     await Promise.resolve()
     await Promise.resolve()
     await Promise.resolve()
+    await new Promise<void>((resolve) => setTimeout(resolve, 0))
   })
 }