Problem:
after https://github.com/neovim/neovim/pull/32719, `gf` error in lua:
```
E15: Invalid expression: "v:lua.require"vim._ftplugin.lua".includeexpr()"
E447: Can't find file "vim._ftplugin.lua" in path
```
Solution:
* use single quote (no idea why there's two pair double quote in
expression).
* add missing `v:fname`.