runtime(doc): fix typo in version9.txt nrformat -> nrformats

This blocks K from finding the keyword

closes: #15726

Signed-off-by: hseg <gesh@gesh.uni.cx>
Signed-off-by: Christian Brabandt <cb@256bit.org>

runtime/doc/version9.txt

@@ -1,4 +1,4 @@
-*version9.txt*  For Vim version 9.1.  Last change: 2024 Aug 23
+*version9.txt*  For Vim version 9.1.  Last change: 2024 Sep 23
 
 
 		  VIM REFERENCE MANUAL    by Bram Moolenaar
@@ -41577,7 +41577,7 @@ Changed~
 - the default for 'commentstring' contains whitespace padding to have
   automatic comments look nicer |comment-install|
 - 'completeopt' is now a |global-local| option.
-- 'nrformat' accepts the new "blank" suboption, to determine a signed or
+- 'nrformats' accepts the new "blank" suboption, to determine a signed or
   unsigned number based on whitespace in front of a minus sign.
 - allow to specify a priority when defining a new sign |:sign-define|
 - provide information about function arguments using the get(func, "arity")