Depends on the direction the fan is facing. If it’s blowing towards you, that increases air pressure in front of it, which means more things for photons to interact with and a lower speed of light, thus slower wifi. Away from you would decrease the pressure and result in faster wifi due to the increased speed of light. Theoretically at least. I don’t think this effect is measurable.

Edit: thinking about it, the electromagnetic noise from a fan motor would likely be worse than the benefit. You might even be able to detect that