How does composition of air affect vapor saturation limit?
I agree with "repurposer"'s comment that the saturation limit would be independent of the composition of the air.

It would just be a function of the partial vapour pressure of water.

$K_{p}=p_{H_2O}$, where $K_p$ is the equilibrium constant in pressure terms.

Consider this case similar to that of aqueous tension - it depends only on the temperature of the system, and not the other (non-reacting) components.
Whenever we want to find the pressure of the dry gas, i.e. pressure of the mixture of gases $-$ the pressure due to the water vapour.

Hope this helps!