input: Write a python function to fetch the latest COVID-19 data from a given URL and save it into a CSV file.
  assert fetch_covid_data('https://raw.githubusercontent.com/CSSEGISandData/COVID-19/master/csse_covid_19_data/csse_covid_19_daily_reports/04-01-20', 'covid_data.csv') == True
  assert os.path.exists('covid_data.csv') == True
output: def fetch_covid_data(url, filename):
      import requests
      import csv
  
      try:
          response = requests.get(url)
          response.raise_for_status()  # Ensure we notice bad responses
  
          with open(filename, 'w', newline='') as csvfile:
              csvfile.write(response.text)
  
          return True
      except Exception as e:
          print(f"An error occurred: {e}")
          return False