I know cedar is not bird safe and the smell from it is an irritant to birds as well as it definitely repels insects which I assume is from some kind of toxicity factors from its oils/scent but this wrapping fish in cedar to cook is something I am not familiar with at all.
A quick google of cedar wood and bird safety will bring up many hits that all say it is dangerous and it can kill them- here is the exact wording from the first hit I got " Cedar bedding and cedar oil are known to irritate birds' delicate respiratory systems, and at high doses, can actually kill them. "
I am not sure how much natural oil and scent is released from the wrapping and cooking of fish in cedar but after knowing it was used as coat hangers, in closets and also for building materials as its scent killed off insects therefore protecting the structure I personally would be hesitant to use it.