rustbuild: "changelog-seen = 1" breaks config.toml

[matthiaskrgr]

warning: x.py has made several changes recently you may want to look at
help: consider looking at the changes in `src/bootstrap/CHANGELOG.md`
note: to silence this warning, add `changelog-seen = 1` to `config.toml`

So I skipped through the changelog and added changelog-seen = 1 to the end of my config toml but this broke x.py:

failed to parse TOML configuration 'config.toml': unknown field `changelog-seen`, expected one of `sign-folder`, `gpg-password-file`, `upload-addr`, `src-tarball`, `missing-tools` for key `dist` at line 522 column 1

[matthiaskrgr]

Apparently the script wants it at the beginning of the toml file, the warning message should says so 🙄