fix(jsonapi): exclude relations from openapi attributes schema

[soyuka]

Q	A
Branch?	4.3
Tickets	Fixes #8308
License	MIT

Problem

For resources using the JSON:API format, the generated OpenAPI schema documents relation properties twice: correctly as resource linkage under relationships, and incorrectly as a full nested object under attributes. The attributes variant never appears in an actual JSON:API response, so the generated spec misrepresents the API. The buggy schema also exposes id where a real response exposes _id.

Root cause

Regression from 79edced ("fix(json-schema): share invariable sub-schemas", shipped in 4.2.0). It replaced the relation-excluding attributes array with a blanket $ref to the full resource schema:

-        $replacement['attributes']['properties'] = $attributes;
+        $replacement['attributes'] = ['$ref' => $currentRef];

buildDefinitionPropertiesSchema() already builds a correct $attributes array (relation properties skipped, id renamed to _id), but it became dead code. A second spot in the collection path re-applied the same full $ref.

Fix

• Restore use of the built $attributes array for data.attributes.properties.
• Drop the collection-path attributes.$ref override so collection items reuse the corrected item data schema.

Tests

• New testRelationIsExcludedFromAttributes: relation absent from attributes, present in relationships; _id present, bare id absent.
• Updated two pre-existing assertions that encoded the buggy $ref behavior.