Gatsby v5 support

### Feature description

Currently this plugin does not work with Gatsby v5

### Motivating example

When running with gastby v5 this error appears:

```
"gatsby-source-pg" threw an error while running the createSchemaCustomization lifecycle:

Cannot use GraphQLObjectType "{ name: "PostGraphile", description: "PostGraphile Query type, gives access to data from PostgreSQL", isTypeOf: undefined,
extensions: {}, astNode: undefined, extensionASTNodes: [], _fields: [function], _interfaces: [function] }" from another module or realm.

Missing onError handler for invocation 'building-schema', error was 'Error: Cannot create as TypeComposer the following value:
GraphQLScalarType({ name: "Date", description: "A date string, such as 2007-12-03, compliant with the ISO 8601 standard for representation of dates and
times using the Gregorian calendar.", specifiedByURL: undefined, serialize: [function String], parseValue: [function String], parseLiteral: [function
parseLiteral], extensions: { }, astNode: undefined, extensionASTNodes: [] }).'. Stacktrace was 'Error: Cannot create as TypeComposer the following value:
GraphQLScalarType({ name: "Date", description: "A date string, such as 2007-12-03, compliant with the ISO 8601 standard for representation of dates and
times using the Gregorian calendar.", specifiedByURL: undefined, serialize: [function String], parseValue: [function String], parseLiteral: [function
parseLiteral], extensions: { }, astNode: undefined, extensionASTNodes: [] }).
```

### Breaking changes

### Supporting development

I [tick all that apply]:

- [x] am interested in building this feature myself
- [x] am interested in collaborating on building this feature
- [x] am willing to help testing this feature before it's released
- [ ] am willing to write a test-driven test suite for this feature (before it exists)
- [ ] am a [Graphile sponsor](https://www.graphile.org/sponsor/) ❤️
- [ ] have an active [support or consultancy contract](https://www.graphile.org/support/) with Graphile