Update Who's Using Ruff? section to include Godot

[Chubercik]

Summary

• Ever since Replace black formatter with ruff godotengine/godot#90457 was merged into the master branch, Godot has been using ruff for linting and formatting Python files. As such, this PR adds Godot to the "Who's Using Ruff?" section of the main README.md file.

Test Plan

• N/A

[charliermarsh]

Nice, thanks!