That one immediately rang false to me, because Latin doesn't have a word that corresponds to the English "religion," in the sense of a body of beliefs that could be considered true or false. The Latin word "religio" means public rituals and duties, including those to the gods (it's closely related to the word "obligation").
The actual quote appears to be from the 18th century historian Edward Gibbon, at least according to an archeologist on Quora:
"It’s not to be found in Seneca. It’s Edward Gibbon (1776):
“The various modes of worship which prevailed in the Roman world were all considered by the people as equally true; by the philosopher as equally false; and by the magistrate as equally useful. And thus toleration produced not only mutual indulgence, but even religious concord." (Edward Gibbon, The Decline and Fall of the Roman Empire, Vol I, (New York: The Modern Library, 1995), p1."
The quote represents 18th century Enlightenment thinking, not 1st century Stoicism.