input: Write a function to detect the vowel in a given string. The function should return the first vowel it encounters in the string. If no vowel is found, the function should return None.
  assert vowelCheck("Hello World") == "e"
  assert vowelCheck("grrm") == None
  assert vowelCheck("Python") == "o"
  assert vowelCheck("UAT") == "U"
  assert vowelCheck("sky") == None
output: def vowelCheck(s):
      vowels = "aeiouAEIOU"
      for char in s:
          if char in vowels:
              return char
      return None