Taxing "robots" is silly, mostly because it's impossible to define what a "robot" is in a remotely non-distortionary way or that doesn't require a horde of accountants to argue out.

Taxing "capital", by its monetary value, is much easier, and has a similar effect of promoting labor substitution. It's also universally despised by economists for the obvious reason that accumulating capital increases the return to labor under most models and makes everyone wealthier.

Of course California state politics are notoriously dumb, so who knows what'll happen.