Custom function in fzf_action works only for `GFiles` and `Files`

- [x] I have fzf 0.23.0 or above
- [x] I have read through https://github.com/junegunn/fzf.vim/blob/master/README.md
- [x] I have read through https://github.com/junegunn/fzf/blob/master/README-VIM.md
- [x] I have read through the manual page of fzf (`man fzf`)
- [x] I have searched through the existing issues

Custom functions in `fzf_action` don't work for `:Rg`, but works fine for `:GFiles` and `:Files`.
I'm trying to use following configuration:
```vimrc
function! s:vsplit_and_nerdtree_find(lines)
exec "vsplit" a:lines[0]
NERDTreeFind
wincmd p
endfunction

function! s:tab_split_and_nerdtree_find(lines)
exec "tab split" a:lines[0]
NERDTreeFind
wincmd p
endfunction

nmap :GFiles
let g:fzf_action = {
\ 'enter' : function('s:vsplit_and_nerdtree_find'),
\ 'ctrl-t': function('s:tab_split_and_nerdtree_find'),
\ }
let $FZF_DEFAULT_COMMAND='find .'
```

When I use `:Rg` and `enter` or `ctrl-t`, it simply opens up the file in the current buffer.

If I map the actions to non-custom functions, e.g., `tab split`, then everything works as expected.