input: Write a python function to filter out non-alphanumeric characters from a given string using regex.
  assert filter_non_alphanumeric("This input contains \" special characters!") == "Thisinputcontainsspecialcharacters"
  assert filter_non_alphanumeric("Hello, World!") == "HelloWorld"
  assert filter_non_alphanumeric("123-456-7890") == "1234567890"
  assert filter_non_alphanumeric("No special_characters_here.") == "Nospecialcharactershere"
output: import re
  
  def filter_non_alphanumeric(s):
      return re.sub(r'[^a-zA-Z0-9]', '', s)