input: Write a python function to extract keywords from a webpage using BeautifulSoup.
  assert extract_keywords('https://www.example.com/', 'example') == ['Example Domain', 'This domain is for use in illustrative examples in documents.']
  assert extract_keywords('https://www.wikipedia.org/', 'Wikipedia') == ['Wikipedia', 'The Free Encyclopedia']
  assert extract_keywords('https://www.python.org/', 'Python') == ['Welcome to Python.org', 'The official home of the Python Programming Language']
output: def extract_keywords(url, keyword):
      import requests
      from bs4 import BeautifulSoup
      
      response = requests.get(url)
      response.raise_for_status()
      
      soup = BeautifulSoup(response.content, 'html.parser')
      text = soup.get_text()
      
      keywords = [line.strip() for line in text.split('\n') if keyword.lower() in line.lower()]
      
      return keywords