input: Write a python function to retrieve user emails from a given list of user dictionaries.
  assert get_user_emails([{'id': 1, 'name': 'John Smith', 'email': 'john.smith@example.com'}, {'id': 2, 'name': 'Jane Doe', 'email': 'jane.doe@example.com'}]) == ['john.smith@example.com', 'jane.doe@example.com']
  assert get_user_emails([{'id': 3, 'name': 'Alice Brown', 'email': 'alice.brown@example.com'}, {'id': 4, 'name': 'Bob White', 'email': 'bob.white@example.com'}]) == ['alice.brown@example.com', 'bob.white@example.com']
  assert get_user_emails([{'id': 5, 'name': 'Charlie Black', 'email': 'charlie.black@example.com'}]) == ['charlie.black@example.com']
output: def get_user_emails(users):
      return [user['email'] for user in users]