Based on the available evidence, I think the number is close to zero.
>Restaurants have been mandated by the state to impose certain regulations and hygiene measures. They follow the general principles of harm reduction that Monica Gandhi[0], an infectious disease expert at UCSF, goes by: masks, distancing, ventilation and hand hygiene. "There is no evidence that I can find anywhere in the world that outdoor dining with those four procedures in play increases the risk of COVID-19," she said. [1]
So there seems to be no evidence that banning outdoor dining is going to do anything positive in stopping the spread, though we know for certain it will have destructive effects on people's well being and the economy.
[0] https://en.wikipedia.org/wiki/Monica_Gandhi
[1] https://www.houstonchronicle.com/bayarea/article/Is-outdoor-...