input: Write a python function to count occurrences of a word in a given string.
  assert count_word_occurrences("Welcome to my website website", "website") == 2
  assert count_word_occurrences("Hello world, hello universe", "hello") == 1
  assert count_word_occurrences("test test test test", "test") == 4
output: def count_word_occurrences(s, word):
      return s.lower().split().count(word.lower())