Improve test failure message

A test failure looks like this:

```
ERROR interface_tester.interface_test:runner.py:55 Failed check 3: validating schema on scene output: 2 validation errors for ProviderSchema
app -> url
field required (type=value_error.missing)
app -> ingesters -> 0 -> protocol
field required (type=value_error.missing)
```

It could be handy if there also was:
- A link to the schema / doc / test.
- More detailed context. It is not clear from "validation errors for ProviderSchema" what was being tested. Does it mean: "a stand-in requirer was not able to parse what the lib's TracingProvider rendered"?

Start at runner.py:55, where the shown failure is reported, and trace how ProviderSchema validation errors are formatted. Reproduce the scene-output failure and determine what schema, documentation, or test links and contextual explanation are available; done means the message provides the requested context and useful link without losing the validation details.

Written by the indexing model from the issue text.