input: Write a python function to read a pickle file and return its content.
  assert read_pickle('example1.pkl') == {'a': 1, 'b': 2}
  assert read_pickle('example2.pkl') == [1, 2, 3, 4, 5]
output: def read_pickle(filename):
      import pickle
      with open(filename, 'rb') as file:
          return pickle.load(file)