input: Write a python function to count the number of vowels in a given text.
  assert count_vowels("hello world") == 3
  assert count_vowels("AEIOUaeiou") == 10
  assert count_vowels("Python Programming") == 4
output: def count_vowels(text):
      vowels = "aeiouAEIOU"
      return sum(1 for char in text if char in vowels)