input: Write a python function to sort a list of Student objects by their grades in ascending order.
  assert sort_students_by_grade([Student("Alice", 85), Student("Bob", 75), Student("Charlie", 95)])[0].name == "Bob"
  assert sort_students_by_grade([Student("Alice", 85), Student("Bob", 75), Student("Charlie", 95)])[1].name == "Alice"
  assert sort_students_by_grade([Student("Alice", 85), Student("Bob", 75), Student("Charlie", 95)])[2].name == "Charlie"
  assert sort_students_by_grade([Student("Alice", 90), Student("Bob", 90), Student("Charlie", 85)])[0].name == "Charlie"
output: def sort_students_by_grade(students):
      return sorted(students, key=lambda student: student.grade)