vim-patch:9.1.1194: filetype: false positive help filetype detection

Problem:  filetype: false positive help filetype detection
Solution: Only detect a file as help if modeline appears either at start
          of line or is preceded by whitespace (zeertzjq).

closes: vim/vim#16845

6763b0ee95

runtime/lua/vim/filetype.lua

@@ -2417,7 +2417,7 @@ local pattern = {
     ['^%.?gtkrc'] = starsetf('gtkrc'),
     ['/doc/.*%.txt$'] = function(_, bufnr)
       local line = M._getline(bufnr, -1)
-      local ml = line:find('vim:')
+      local ml = line:find('^vim:') or line:find('%svim:')
       if ml and M._matchregex(line:sub(ml), [[\<\(ft\|filetype\)=help\>]]) then
         return 'help'
       end