fix: fix indent-blankline config

[lukas-reineke]

nvim-lua#443 updated to v3, but now the configuration is wrong.
char and show_trailing_blankline_indent are not valid options like this anymore.

show_trailing_blankline_indent is removed, it's always false now.

If you want to keep char, it would be opts = { indent = { char = "┊" } }, but I recommend leaving the default, or it looks weird with the scope.

vs