makeProcessSchemaPlugin and @graphql-tools/merge
Hi and thanks for the good work on Postgraphile,

The following plugin (which should do nothing) seems to break connection fields (it looks like it works on single items). I'm not familiar enough with the low-level GraphQL implementations, so I ask here if that's something someone struggled with before ?

```js
import { mergeSchemas } from "@graphql-tools/merge";

const plugin = makeProcessSchemaPlugin((schema) =>
  mergeSchemas({
    schemas: [schema],
  })
);
```

Cheers