input: Write a python function to calculate the total cost of grocery items given a list of GroceryItem objects.
  assert calculate_total_cost([GroceryItem("Apple", 0.5, 10), GroceryItem("Banana", 0.2, 20)]) == 9.0
  assert calculate_total_cost([GroceryItem("Milk", 1.5, 2), GroceryItem("Bread", 2.0, 1)]) == 5.0
  assert calculate_total_cost([GroceryItem("Eggs", 0.1, 30), GroceryItem("Juice", 3.0, 1)]) == 6.0
output: def calculate_total_cost(grocery_items):
      return sum(item.price * item.quantity for item in grocery_items)