tramp-yesno-prompt-regexp

tramp-yesno-prompt-regexp is a variable defined in `tramp.el'.
Its value is

"\\(Are you sure you want to continue connecting (yes/no)\\?\\)\\s-*"

Documentation:
Regular expression matching all yes/no queries which need to be confirmed.
The confirmation should be done with yes or no.
The regexp should match at end of buffer.
See also `tramp-yn-prompt-regexp'.

You can customize this variable.