input: def replace_all_occurrences(str: str, char: str, replacement: str) -> str:
      """
      Replace all occurrences of a specified character in a given string with the provided replacement character.
      
      >>> replace_all_occurrences("Hello World!", 'l', 'X')
      'HeXXo WorXd!'
      >>> replace_all_occurrences("Good morning!", 'o', 'a')
      'Gaad marninga!'
      """
output:     return str.replace(char, replacement)