input: Write a python function to count the occurrences of a specific character in a given string.
  assert count_char_in_string("Hello, World!", "l") == 3
  assert count_char_in_string("abcdefg", "a") == 1
  assert count_char_in_string("mississippi", "s") == 4
output: def count_char_in_string(s: str, char: str) -> int:
      return s.count(char)