The slow-binding test used a 250 ms compute budget, which is below the instrumented worker startup cost seen intermittently in the four-worker Windows coverage job. That startup activity could exhaust the budget before the program settled into the awaited binding, making the timing assertion depend on runner load.
Use a one-second compute budget and a two-second binding delay. The awaited wall time still exceeds the busy-time allowance by a clear factor, so the test continues to prove that binding wait time is not charged while leaving enough headroom for worker initialization under coverage.