input: Write a python function to sort a list of Employee objects by salary in ascending order.
  assert sort_employees_by_salary([Employee("Alice", 30, 70000), Employee("Bob", 24, 50000), Employee("Charlie", 28, 60000)]) == [Employee("Bob", 24, 50000), Employee("Charlie", 28, 60000), Employee("Alice", 30, 70000)]
  assert sort_employees_by_salary([Employee("Dave", 35, 80000), Employee("Eve", 29, 55000), Employee("Frank", 31, 75000)]) == [Employee("Eve", 29, 55000), Employee("Frank", 31, 75000), Employee("Dave", 35, 80000)]
  assert sort_employees_by_salary([Employee("George", 40, 90000), Employee("Hank", 25, 40000), Employee("Ivy", 33, 85000)]) == [Employee("Hank", 25, 40000), Employee("Ivy", 33, 85000), Employee("George", 40, 90000)]
output: def sort_employees_by_salary(employees):
      return sorted(employees, key=lambda x: x.salary)