bug#32546: 26.1: checkdoc uses smart quotes

[Alex Branham]

>From emacs -Q, write:

(defun foo ()
  "A major-mode."
  (+ 1 1))

and do M-x checkdoc. It'll complain about major-mode needing to be
quoted. Hit "f" and you get:

(defun foo ()
  "A ‘major-mode’."
  (+ 1 1))

instead of

(defun foo ()
  "A `major-mode'."
  (+ 1 1))

I know that docstrings you see via e.g. C-h f use "smart" quotes now,
but I found it surprising that they're getting put into docstrings
themselves.

Thanks,
Alex