fix(package): indentation to be 2 spaces as elsewhere

[max-nextcloud]

#5268 changed the indentation of package.json to tabs from spaces. This makes it so tabs will also be used for package-lock.json

This way backporting PRs that touch package.json or package-lock.json will always require manual steps.

Server uses spaces, deck uses spaces. (just two somewhat random samples)
So I think it's probably best to revert.