Yes you can leave garlic bread out overnight.
Actually garlic bread is best stored out at room temperature and not in the refrigerator.
There's no need to refrigerate garlic bread and it will stay fresher and last longer out on the counter or at room temperature.
It's actually not recommended to refrigerate the garlic bread.
If you do refrigerate the garlic bread the garlic bread can dry out in the refrigerate and become stale much quicker and even crusty.
So it's better to leave the garlic bread out at room temperature and never refrigerate it.