input: Write a python function to find the first occurrence of a character in a string.
  assert find_first_occurrence("Hello World", 'l') == 2
  assert find_first_occurrence("Hello World", 'o') == 4
  assert find_first_occurrence("Python", 'P') == 0
output: def find_first_occurrence(s: str, ch: str) -> int:
      return s.find(ch)