runtime(help): Update syntax

Match Vim9 return types in builtin function specifications.

closes: #18477

Signed-off-by: Doug Kearns <[email protected]>
Signed-off-by: Christian Brabandt <[email protected]>

Author: dkearns

runtime/syntax/help.vim

@@ -1,7 +1,7 @@
 " Vim syntax file
 " Language:		Vim help file
 " Maintainer:		Doug Kearns <[email protected]>
-" Last Change:		2025 Sep 29
+" Last Change:		2025 Oct 03
 " Former Maintainer:	Bram Moolenaar <[email protected]>
 
 " Quit when a (custom) syntax file was already loaded
@@ -62,6 +62,14 @@ if has_key(g:help_example_languages, "vim9")
   syn cluster helpExampleHighlight_vim9 add=vim9LegacyHeader_HelpExample
 endif
 
+" builtin.txt
+syn region helpReturnType
+      \ start="^\t\tReturn type: "
+      \ end="^$"
+      \ contains=@vimType,helpHyperTextJump,helpSpecial
+      \ transparent
+syn match helpSpecial		contained "{type}" containedin=vimCompoundType
+
 if has("ebcdic")
   syn match helpHyperTextJump	"\\\@<!|[^"*|]\+|" contains=helpBar
   syn match helpHyperTextEntry	"\*[^"*|]\+\*\s"he=e-1 contains=helpStar