input: Write a python function to remove all non-alphabetic characters from a given string.
  assert remove_non_alphabetic("This text contains some non-alphabetic characters, like “%.”") == "This text contains some nonalphabetic characters like "
  assert remove_non_alphabetic("Hello, World! 123") == "Hello World "
  assert remove_non_alphabetic("Python3.8") == "Python"
  assert remove_non_alphabetic("No special characters") == "No special characters"
output: def remove_non_alphabetic(s):
      return ''.join(char if char.isalpha() or char.isspace() else '' for char in s)