vim-patch: bump VIM_VERSION from 8.0 => 8.1 #20762

There are 6 remaining 8.0.x patches, tracked in:
https://github.com/neovim/neovim/issues/5431

scripts/gen_help_html.lua

@@ -339,6 +339,7 @@ local function validate_link(node, bufnr, fname)
   return helppage, tagname, ignored
 end
 
+-- TODO: port the logic from scripts/check_urls.vim
 local function validate_url(text, fname)
   local ignored = false
   if vim.fs.basename(fname) == 'pi_netrw.txt' then