Meta: Fix CI lint checks

[Totto16]

I noticed, that the Meta/lint-gn.sh script found errors in the CI, but it just formatted the files and reported no failure.

Now it uses --dry-run as an argument, so that gn format itself exits with a non-zero exit code, if it finds unformatted files.

This adds the option --overwrite-inplace to the script, so that you can also format git files or manual specified files, and not just report failures in them.

[AtkinsSJ]

Can you swap the order of the commits? It's nice if things always pass.