patch 9.0.1396: sort(list, 'N') does not work in Vim9 script context

Problem:    sort(list, 'N') does not work in Vim9 script context.
Solution:   Convert string to number without giving an error. (closes #12061)
diff --git a/runtime/doc/builtin.txt b/runtime/doc/builtin.txt
index a695547..da2bf32 100644
--- a/runtime/doc/builtin.txt
+++ b/runtime/doc/builtin.txt
@@ -8641,8 +8641,9 @@
 
 		When {how} is given and it is 'n' then all items will be
 		sorted numerical (Implementation detail: this uses the
-		strtod() function to parse numbers, Strings, Lists, Dicts and
-		Funcrefs will be considered as being 0).
+		strtod() function to parse numbers.  Strings, Lists, Dicts and
+		Funcrefs will be considered as being 0).  Note that this won't
+		sort a list of strings with numbers!
 
 		When {how} is given and it is 'N' then all items will be
 		sorted numerical. This is like 'n' but a string containing