[errors] s/form state/action state (#35790)

Noticed `useActionState` error still refers to "form state" while
writing the docs.

DiffTrain build for [93882bd40ee48dc6d072dfc0b6cc7801fac1be31](https://github.com/facebook/react/commit/93882bd40ee48dc6d072dfc0b6cc7801fac1be31)