Fix code for newline-and-indent in skeleton language.

The code for this is the symbol 'n', which is usually spelled as '\n'
here, not the character ?\n.

* doc/misc/autotype.texi (Skeleton Language): Fix item for
newline-and-indent.
1 job for emacs-27 in 63 minutes and 36 seconds (queued for 3 seconds)
Status Job ID Name Coverage
  Test
passed #18683
test-all

01:03:36