input: Write a python function to calculate the stability of a string based on the vowel count and length.
  assert checkStability("This is a test sentence!") == 0.32
  assert checkStability("Hello World") == 0.27
  assert checkStability("A quick brown fox") == 0.25
output: def checkStability(s: str) -> float:
      vowels = "aeiouAEIOU"
      vowel_count = sum(1 for char in s if char in vowels)
      length = len(s)
      if length == 0:
          return 0.0
      return round(vowel_count / length, 2)