runtime: set 'cpoptions' for line-continuation in various runtime files

closes: #17121

Signed-off-by: Eisuke Kawashima <e-kwsm@users.noreply.github.com>
Signed-off-by: Christian Brabandt <cb@256bit.org>
diff --git a/runtime/ftplugin/tera.vim b/runtime/ftplugin/tera.vim
index 65bae70..ce4134a 100644
--- a/runtime/ftplugin/tera.vim
+++ b/runtime/ftplugin/tera.vim
@@ -2,12 +2,16 @@
 " Language:             Tera
 " Maintainer:           Muntasir Mahmud <muntasir.joypurhat@gmail.com>
 " Last Change:          2025 Mar 08
+" 2025 Apr 16 by Vim Project (set 'cpoptions' for line continuation, #17121)
 
 if exists("b:did_ftplugin")
   finish
 endif
 let b:did_ftplugin = 1
 
+let s:cpo_save = &cpo
+set cpo&vim
+
 setlocal autoindent
 
 setlocal commentstring={#\ %s\ #}
@@ -28,3 +32,6 @@
 let b:undo_ftplugin = "setlocal autoindent< commentstring< comments< " ..
       \ "includeexpr< suffixesadd< expandtab< shiftwidth< softtabstop<"
 let b:undo_ftplugin .= "|unlet! b:match_ignorecase b:match_words"
+
+let &cpo = s:cpo_save
+unlet s:cpo_save