bug#51777: 27.2; Markup Typo in Elisp Introduction

[Nicolas Semrau]

In line 5804 of the file
/doc/lispintro/emacs-lisp-intro.texi on the emacs-28 branch the line reads

"and not just to the name of a buffer, the @code{insert-buffer
function}".

The closing parenthesis of the "@code" markup falsely encloses the word
"function" in it.  It should be behind "insert-buffer" instead.

On master, the same error is on line 5821 of that file.