input: Write a function to accept a string as an input and return the total number of vowels in the string.
  assert count_vowels("Hello, World!")==3
  assert count_vowels("Python Programming")==4
  assert count_vowels("AEIOU")==5
  assert count_vowels("")==0
  assert count_vowels("Thr33 m@n in a d3p0tt!")==5
output: def count_vowels(s):
      vowels = "aeiouAEIOU"
      count = 0
      for char in s:
          if char in vowels:
              count += 1
      return count