runtime(doc): mention hl-PreInsert in version9.txt

Signed-off-by: Christian Brabandt <cb@256bit.org>

Author: chrisbra

runtime/doc/version9.txt

@@ -1,4 +1,4 @@
-*version9.txt*  For Vim version 9.1.  Last change: 2025 Sep 08
+*version9.txt*  For Vim version 9.1.  Last change: 2025 Sep 09
 
 
 		  VIM REFERENCE MANUAL    by Bram Moolenaar
@@ -41822,6 +41822,7 @@ Highlighting: ~
 |hl-PmenuMatch|		Popup menu: highlighting of matched text
 |hl-PmenuMatchSel|	Popup menu: highlighting of matched text in selected
 			line
+|hl-PreInsert|		highlighting for completion preinserted text
 |hl-TabPanel|		|tabpanel|: not active tab page label
 |hl-TabPanelFill|	|tabpanel|: filler space
 |hl-TabPanelSel|	|tabpanel|: active tab page label