fix: no_blocking.test.w flaking (#4921)

Fixes #4874

## Checklist

- [ ] Title matches [Winglang's style guide](https://www.winglang.io/contributing/start-here/pull_requests#how-are-pull-request-titles-formatted)
- [ ] Description explains motivation and solution
- [ ] Tests added (always)
- [ ] Docs updated (only required for features)
- [ ] Added `pr/e2e-full` label if this feature requires end-to-end testing

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examples/tests/sdk_tests/topic/no_blocking.test.w

@@ -18,8 +18,8 @@ test "topic subscribers are invoked without blocking" {
   // since the subscriber sleeps for 3 seconds, the counter should still be 0
   assert(counter.peek() == 0);
 
-  util.sleep(6s);
-
   // after a while, the counter should be 1
+  util.waitUntil(inflight () => { return counter.peek() == 1; }, interval: 1s, timeout: 30s);
+
   assert(counter.peek() == 1);
 }