runtime(vim): fix syntax vim bug (Close #14858) (#14861)

Signed-off-by: h-east <h.east.727@gmail.com>
Signed-off-by: Christian Brabandt <cb@256bit.org>

runtime/syntax/generator/gen_syntax_vim.vim

@@ -464,6 +464,10 @@ function! s:parse_vim_hlgroup(li)
 		let item.type = 'both'
 		call add(a:li, copy(item))
 
+		" "Conceal" is an option and cannot be used as keyword, so remove it.
+		" (Separately specified as 'syn match' in vim.vim.base).
+		call filter(a:li, {idx, val -> val.name !=# 'Conceal'})
+
 		quit!
 
 		if empty(a:li)

runtime/syntax/generator/vim.vim.base

@@ -70,6 +70,7 @@ syn keyword vimGroup contained	Comment Constant String Character Number Boolean
 
 " Default highlighting groups {{{2
 " GEN_SYN_VIM: vimHLGroup, START_STR='syn keyword vimHLGroup contained', END_STR=''
+syn match vimHLGroup contained "\<Conceal\>"
 syn case match
 
 " Function Names {{{2