Tests should expose breaking changes to source data structure

[rjsparks]

There are several places where the bibxml code is having to adjust to changes in the relaton source data, and tests didn't show that things had become disconnected.

This needs to be addressed in addition to whatever actions come from the conversations around versioning libraries to help avoid encountering breaking changes by surprise in the future.

References: https://github.com/ietf-tools/bibxml-service/pull/282#pullrequestreview-1090992508 https://github.com/ietf-tools/bibxml-service/issues/283