input: Write a python function to web scrape news headlines from CNN and return them as a list of strings.
  assert isinstance(scrape_cnn(), list)
  assert all(isinstance(headline, str) for headline in scrape_cnn())
  assert len(scrape_cnn()) > 0
output: def scrape_cnn():
      import requests
      from bs4 import BeautifulSoup
  
      url = "https://www.cnn.com"
      response = requests.get(url)
      soup = BeautifulSoup(response.content, "html.parser")
  
      headlines = []
      for item in soup.find_all("h3", class_="cd__headline"):
          headline = item.get_text(strip=True)
          if headline:
              headlines.append(headline)
  
      return headlines