patch 9.1.0469: Cannot have buffer-local value for 'completeopt'

Problem:  Cannot have buffer-local value for 'completeopt'
          (Nick Jensen).
Solution: Make 'completeopt' global-local (zeertzjq).

Also for some reason test Test_ColonEight_MultiByte seems to be failing
sporadically now. Let's mark it as flaky.

fixes: #5487
closes: #14922

Signed-off-by: zeertzjq <zeertzjq@outlook.com>
Signed-off-by: Christian Brabandt <cb@256bit.org>
diff --git a/runtime/doc/options.txt b/runtime/doc/options.txt
index 57fefa2..655fd6c 100644
--- a/runtime/doc/options.txt
+++ b/runtime/doc/options.txt
@@ -1,4 +1,4 @@
-*options.txt*	For Vim version 9.1.  Last change: 2024 Jun 04
+*options.txt*	For Vim version 9.1.  Last change: 2024 Jun 05
 
 
 		  VIM REFERENCE MANUAL	  by Bram Moolenaar
@@ -2101,7 +2101,7 @@
 
 						*'completeopt'* *'cot'*
 'completeopt' 'cot'	string	(default: "menu,preview")
-			global
+			global or local to buffer |global-local|
 	A comma-separated list of options for Insert mode completion
 	|ins-completion|.  The supported values are:
 
diff --git a/runtime/doc/version9.txt b/runtime/doc/version9.txt
index 07c416a..6edb889 100644
--- a/runtime/doc/version9.txt
+++ b/runtime/doc/version9.txt
@@ -1,4 +1,4 @@
-*version9.txt*  For Vim version 9.1.  Last change: 2024 Jun 03
+*version9.txt*  For Vim version 9.1.  Last change: 2024 Jun 05
 
 
 		  VIM REFERENCE MANUAL    by Bram Moolenaar
@@ -41567,6 +41567,7 @@
 - use 'smoothscroll' logic for CTRL-D and CTRL-U for half-pagewise scrolling
 - the default for 'commentstring' contains whitespace padding to have
   automatic comments look nicer |comment-install|
+- 'completeopt' is now a |global-local| option.
 
 							*added-9.2*
 Added ~
diff --git a/runtime/optwin.vim b/runtime/optwin.vim
index d3e1605..f218ffb 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:	2023 Aug 31
+" Last Change:	2024 Jun 05
 " Former Maintainer:	Bram Moolenaar <Bram@vim.org>
 
 " If there already is an option window, jump to that one.
@@ -846,7 +846,7 @@
   call append("$", "\t" .. s:local_to_buffer)
   call <SID>OptionL("cpt")
   call <SID>AddOption("completeopt", gettext("whether to use a popup menu for Insert mode completion"))
-  call <SID>OptionG("cot", &cot)
+  call <SID>OptionL("cot")
   if exists("+completepopup")
     call <SID>AddOption("completepopup", gettext("options for the Insert mode completion info popup"))
     call <SID>OptionG("cpp", &cpp)