Can a turbo charger ruin a transmission?

Yes and no, depends on the circumstances.

If the turbo charger boosts the engine output past what the transmission was designed to withstand it can cause failure.

Every manufacturer knows what their transmissions can hold and usually publishes the ratings.

If the vehicle came from the factory with a turbo installed however, the transmission was built to take the extra output. Not to say things don't break, but it probably isn't directly related to the turbo.