input: Write a python function to find the most common consecutive word pair in a list of words.
  assert most_common_pair(["this", "is", "a", "test", "this", "is", "only", "a", "test"]) == "this is"
  assert most_common_pair(["hello", "world", "hello", "world", "hello"]) == "hello world"
  assert most_common_pair(["one", "fish", "two", "fish", "red", "fish", "blue", "fish"]) == "fish blue"
output: def most_common_pair(words):
      from collections import Counter
      
      pairs = [f"{words[i]} {words[i+1]}" for i in range(len(words) - 1)]
      most_common = Counter(pairs).most_common(1)
      
      return most_common[0][0] if most_common else None