Cars turn into ovens in no time at all. It doesn’t even need full sunlight to be dangerous for dogs in cars. The windows down may not be sufficient.
Park in the shade and be aware of when the shade might move round to expose your car to sunlight.
Never pop away from the car unless you know how long you will be.
Don’t take your dog with you if you can’t be sure it will be safe to do so.
Tying dogs to cars to avoid the sun problem has also resulted in devastating accidents, when folk have forgotten they’ve done so and driven off.