input: Write a python function to preprocess text data by removing special characters and converting to lowercase.
  assert preprocess_text("Hello, World!") == "hello world"
  assert preprocess_text("Python@3.9") == "python39"
  assert preprocess_text("Data Science!") == "data science"
output: def preprocess_text(text):
      import re
      text = re.sub(r'[^a-zA-Z0-9\s]', '', text)
      return text.lower()