input: Write a python function to count the frequency of elements in a list.
  assert count_frequency([1, 4, 1, 4, 4, 4, 9, 7]) == {1: 2, 4: 4, 9: 1, 7: 1}
  assert count_frequency([5, 5, 5, 3, 3, 2]) == {5: 3, 3: 2, 2: 1}
  assert count_frequency([10, 20, 20, 30, 30, 30]) == {10: 1, 20: 2, 30: 3}
output: def count_frequency(lst):
      frequency = {}
      for item in lst:
          if item in frequency:
              frequency[item] += 1
          else:
              frequency[item] = 1
      return frequency