input: Write a function to calculate the running average of temperature readings.
  assert running_average([('10:00', 21), ('10:10', 22), ('10:20', 21), ('10:30', 19), ('10:40', 24), ('10:50', 21)]) == [21.0, 21.5, 21.333333333333332, 20.75, 21.4, 21.333333333333332]
  assert running_average([('09:00', 18), ('09:15', 20), ('09:30', 22), ('09:45', 21)]) == [18.0, 19.0, 20.0, 20.25]
  assert running_average([]) == []
output: def running_average(readings):
      if not readings:
          return []
      
      averages = []
      total = 0
  
      for i, (_, temp) in enumerate(readings):
          total += temp
          averages.append(total / (i + 1))
      
      return averages