Formatter shouldn't write if nothing was changed

[DeeJayLSP]

1. In Godot, open a big project with many scripts
2. In the main folder, run a command like find . -name "*.gd" -exec gdscript-formatter {} \;. This will call the formatter on every single GDScript file in the project.
3. Focus on Godot again. It will reimport every single script.

This implies every script was overwritten, even if already formatted.