Fix: GraphlQL introspection error for publication content

Beim generieren des GraphQL Schemas gibt es folgende Fehlermeldung:

{ "errors": [ { "debugMessage": "Schema must contain unique named types but contains multiple types named \u0022PublicationContent\u0022 (see http:\/\/webonyx.github.io\/graphql-php\/type-system\/#type-registry).", "message": "Internal server error", "extensions": { "category": "internal" }