Some of the errors tests need to have their own schema, so the schema
can do something weird (or even be entirely invalid!). But most can
still share a schema. In this commit I have those indeed share a
schema, to avoid having to have a bunch of copies of mostly the same
schema. While doing so I noticed one error whose location wasn't very
useful, and fixed it.
Test plan: make check
Ben Kraft
d4ec64fef1