rg scanner doesn't work on Windows

[svraka]

The recent changes which introduced directory-form in the rg scanner broke magit-todos on Windows.

With the default settings magit-todos-list starts an rg command, which looks like does it's job but the process keeps running and TODOs aren't inserted in the buffer. With a custom scanner that leaves :directory-form empty but otherwise is identical to the default one, everthing works (and results have a leading ./).

As far as I can tell, the default scanner runs rg <OPTIONS> <PATTERN> ./, while a scanner with empty :directory-form runs rg <OPTIONS> <PATTERN> (without the path at the end). In a shell both commands work, and their output differs in the leading ./.

On macOS with the same config works without any issues. All testing done with Emacs 29.1 and latest MELPA packages.