input: Write a function to count the number of vowels in a given text.
  assert count_vowels("Python is a great language for developers") == 11
  assert count_vowels("Hello World") == 3
  assert count_vowels("BCDFG") == 0
output: def count_vowels(text):
      vowels = "aeiouAEIOU"
      return sum(1 for char in text if char in vowels)