Does the forgiveness of the owner of the money include the person who embezzled it, given that he was part of a group to whom the owner of the money said: "All the money you took is permissible for you"?

Yes, his forgiveness includes you, because his statement: "Gather all Muslim workers" is an indication that signifies generality. He did not ask for the embezzlers to be gathered, but rather intended to absolve everyone without embarrassment. You are obligated to repent with its conditions, except for returning the money, because he has forgiven you for it. It is better that you return what you embezzled to him, and you are not obligated to inform him that it was stolen. Rather, it is permissible to use stratagem or to leave the amount you embezzled from your right in the institution.