input: Write a python function to detect plagiarism between two strings and calculate their similarity percentage.
  assert plagiarism_detector('The quick brown fox', 'The quick brown fox jumps over the lazy dog')==None
  assert plagiarism_detector('Hello World', 'Hello World')==None
  assert plagiarism_detector('Python programming', 'Python coding')==None
output: def plagiarism_detector(text1, text2):
      from difflib import SequenceMatcher
  
      def calculate_similarity(a, b):
          return SequenceMatcher(None, a, b).ratio()
  
      similarity = calculate_similarity(text1, text2)
      if similarity == 1.0:
          return 'Plagiarism detected: 100% similarity'
      else:
          return 'No plagiarism detected'