input: Write a python function to sum all numbers in a given string.
  assert sum_of_numbers_in_string("The numbers are 5 10 and 15") == 30
  assert sum_of_numbers_in_string("4 5 6") == 15
  assert sum_of_numbers_in_string("No numbers here") == 0
output: def sum_of_numbers_in_string(s):
      return sum(int(num) for num in s.split() if num.isdigit())