running anicca twice with same inputs has different outputs

[gr2m]

To reproduce

# download latest `api.github.com.deref.json` and store it as `fixtures/api.github.com.deref-changed.json`
curl https://raw.githubusercontent.com/github/rest-api-description/main/descriptions/api.github.com/dereferenced/api.github.com.deref.json --output fixtures/api.github.com.deref-changed.json
# create diff.json
cargo run --bin cli diff fixtures/api.github.com.deref.json fixtures/api.github.com.deref-changed.json --format json > diff.json
# stage the changes
git add .
# run again
cargo run --bin cli diff fixtures/api.github.com.deref.json fixtures/api.github.com.deref-changed.json --format json > diff.json
# diff.json has been changed, but it should not have
git status