input: Write a python function to scrape life expectancy data from a given URL using BeautifulSoup and requests.
  assert scrape_life_expectancy("http://www.who.int/countries/ind/en/") == 68.3
  assert scrape_life_expectancy("http://www.who.int/countries/usa/en/") == 79.3
output: def scrape_life_expectancy(url):
      import requests
      from bs4 import BeautifulSoup
  
      response = requests.get(url)
      soup = BeautifulSoup(response.content, 'html.parser')
  
      life_expectancy = None
      for div in soup.find_all('div', class_='indicator'):
          if 'Life expectancy at birth' in div.text:
              life_expectancy = float(div.find_next('div', class_='number').text.strip())
              break
      
      return life_expectancy