✅(backend) improve test error

This test was missing the status code check. Without this check
the error that follows does not make sense because the content
returned is not at all what we expect in the following assert
statement.

src/backend/core/tests/documents/test_api_document_versions.py

@@ -229,6 +229,8 @@ def test_api_document_versions_list_authenticated_related_pagination_parent(
     )
 
     content = response.json()
+
+    assert response.status_code == 200
     assert content["is_truncated"] is False
     # The current version is not listed
     assert content["count"] == 3