Could the export-ignore property be used instead? I don't see why something should be in the .crate that if git archive would ignore it too. I just don't want to see cargo grow a menagerie of default exclusions for every forge's hidden directory (sr.ht, foegejo, gitlab) that changes based on the version in use.
As for .gitignore itself, it could be useful to see what may be missing. But again, I think export-ignore is a better source for this.