patch 9.1.1284: not possible to configure pum truncation char

Problem:  not possible to configure the completion menu truncation
          character
Solution: add the "trunc" suboption to the 'fillchars' setting to
          configure the truncation indicator (glepnir).

closes: #17006

Co-authored-by: zeertzjq <zeertzjq@outlook.com>
Signed-off-by: glepnir <glephunter@gmail.com>
Signed-off-by: Christian Brabandt <cb@256bit.org>
diff --git a/runtime/optwin.vim b/runtime/optwin.vim
index 05ea6a2..c5e77af 100644
--- a/runtime/optwin.vim
+++ b/runtime/optwin.vim
@@ -1,7 +1,7 @@
 " These commands create the option window.
 "
 " Maintainer:	The Vim Project <https://github.com/vim/vim>
-" Last Change:	2025 Apr 06
+" Last Change:	2025 Apr 07
 " Former Maintainer:	Bram Moolenaar <Bram@vim.org>
 
 " If there already is an option window, jump to that one.
@@ -371,7 +371,7 @@
 call append("$", " \tset siso=" . &siso)
 call <SID>AddOption("display", gettext("include \"lastline\" to show the last line even if it doesn't fit\ninclude \"uhex\" to show unprintable characters as a hex number"))
 call <SID>OptionG("dy", &dy)
-call <SID>AddOption("fillchars", gettext("characters to use for the status line, folds and filler lines"))
+call <SID>AddOption("fillchars", gettext("characters to use for the status line, folds, diffs, buffer text, filler lines and truncation in the completion menu"))
 call <SID>OptionG("fcs", &fcs)
 call <SID>AddOption("cmdheight", gettext("number of lines used for the command-line"))
 call append("$", " \tset ch=" . &ch)