input: Write a function to count the occurrences of a character in a string.
  assert countOccurences('abcdefg', 'a') == 1
  assert countOccurences('hello world', 'o') == 2
  assert countOccurences('test case', 'e') == 2
output: def countOccurences(s: str, ch: str) -> int:
      return s.count(ch)