input: Write a function to get keys of a dictionary for a given value.
  assert get_keys_by_value(my_dict, 'fruit') == ['apple']
  assert get_keys_by_value(my_dict, 'animal') == ['goat']
  assert get_keys_by_value(my_dict, 'number') == ['three']
output: def get_keys_by_value(my_dict, value):
      return [k for k, v in my_dict.items() if v == value]