g:matchup_treesitter_include_match_words doesn't work for ft=lua

[tunaflsh]

Explain the issue

1. Neovim v.0.12.2
2. Put in init.vim:

   set nocompatible
   
   let &rtp  = '~/.vim/bundle/vim-matchup,' . &rtp
   let &rtp .= ',~/.vim/bundle/vim-matchup/after'
   
   filetype plugin indent on
   syntax enable
   
   let g:matchup_treesitter_include_match_words = v:true
   au FileType lua let b:match_words = '^<<<<<<<:^=======:^>>>>>>>'
   au FileType lua lua vim.treesitter.start()

   Open file.lua:

   cat << EOF > file.lua
   <<<<<<<
   =======
   >>>>>>>
   EOF
   nvim -u init.vim file.lua

3. Expected behavior: everything is highlighted and % cycles through the three lines
4. Observed behavior: doesn't work as expected

[tunaflsh]

Works for filetype=make. So maybe this affects only some languages.