runtime(doc): wrong {str} length limit in matchfuzzy() docs

Problem:  docs say {str} is capped at 256 and longer returns an empty list.
Solution: it's 1024, and {str} plus each candidate are just truncated to
          that, not rejected; fix the text.

closes: #20453

Signed-off-by: glepnir <glephunter@gmail.com>
Signed-off-by: Christian Brabandt <cb@256bit.org>

runtime/doc/builtin.txt

@@ -1,4 +1,4 @@
-*builtin.txt*	For Vim version 9.2.  Last change: 2026 May 31
+*builtin.txt*	For Vim version 9.2.  Last change: 2026 Jun 09
 
 
 		  VIM REFERENCE MANUAL	  by Bram Moolenaar
@@ -7549,15 +7549,15 @@ matchfuzzy({list}, {str} [, {dict}])			*matchfuzzy()*
 				use for fuzzy matching.
 
 		{str} is treated as a literal string and regular expression
-		matching is NOT supported.  The maximum supported {str} length
-		is 256.
+		matching is NOT supported.  Only the first 1024 characters of
+		{str} and of each item in {list} are used for matching;
+		characters beyond that are ignored.
 
 		When {str} has multiple words each separated by white space,
 		then the list of strings that have all the words is returned.
 
 		If there are no matching strings or there is an error, then an
-		empty list is returned.  If length of {str} is greater than
-		256, then returns an empty list.
+		empty list is returned.
 
 		When {limit} is given, matchfuzzy() will find up to this
 		number of matches in {list} and return them in sorted order.