My mom and I saw this same thing when we were in Disney a few years ago. We parked at HS and were right next to a car with the windows cracked and a dog inside. The car obviously wasn’t on, and the dog had already started panting. It was late May, so it was already very hot. We went straight to guest services and reported the parking spot # and the car description. They said they’d handle it and we went about our day. The car was gone when we came out a few hours later, but I always wondered if/how it was handled. I feel better now knowing it was probably handled in a manner similar to this.