input: Write a python function to classify a text into either spam or ham.
  assert classify_spam('Win a $1000 gift card now! Click here!') == 'spam'
  assert classify_spam('Hey, are we still on for lunch today?') == 'ham'
  assert classify_spam('Exclusive offer just for you! Limited time only!') == 'spam'
  assert classify_spam('Your meeting is scheduled for 3 PM tomorrow.') == 'ham'
output: def classify_spam(text):
      spam_keywords = ['win', 'gift', 'click', 'exclusive', 'offer', 'limited', 'time']
      text_lower = text.lower()
      for keyword in spam_keywords:
          if keyword in text_lower:
              return 'spam'
      return 'ham'