input: Write a python function to filter students who have grade 'A'.
  assert filter_students_with_A(student_grades) == ['Adam', 'Aaron']
  assert filter_students_with_A({"John": "B", "Jane": "A", "Jim": "C", "Jill": "A"}) == ['Jane', 'Jill']
  assert filter_students_with_A({"Mark": "B", "Luke": "B", "Matt": "B"}) == []
output: def filter_students_with_A(student_grades):
      return [student for student, grade in student_grades.items() if grade == 'A']