The commit that reordered the chain did not carry the version bump. The
bump was chained after check.sh with &&, the commit after a semicolon, so
a failing check skipped the bump and let the commit through. The tag then
pointed at a tree still calling itself 0.3.0, which the release workflow
asserts against and would have refused.
check.sh was failing because a test names which register is asked first
about an ISBN, which is exactly what changed. It now names the index, for
the reason the reorder happened.