Error highlighting and tooltips stopped working in Graphiql
Running the built-in Graphiql used to provide error highlighting (red squiggles) and error tooltips against the graphql schema. It looked like this (this screenshot is from the [Graphiql live demo](http://graphql.org/swapi-graphql)):

![image](https://user-images.githubusercontent.com/4787751/181846284-456195a0-d6a6-44ee-bae0-ad072bf75bb2.png)

It seems at some point this stopped working in Postgraphile. To make sure it wasn't just my project, I ran through the [docker tutorial](https://www.graphile.org/postgraphile/running-postgraphile-in-docker/) and the error highlighting and tooltips don't work when I hit that Graphiql instance either:

![image](https://user-images.githubusercontent.com/4787751/181846050-ead77115-fc48-489e-a789-f454a12b28c4.png)

Autocomplete (and the explorer and docs when enabled) work OK, so the schema seems to be loading, it's just not doing the error highlighting or tooltips.