[BUG][Spring] 6.x.x generator incorrectly creating dictionaries when using $ref

Description

When migrating from 3.x openapi generator to the 6.x generator, our model objects no longer serialize / deserialize properly. We are using the spring generator.
I have pinpointed the issue to how the generator creates the model objects when creating a dictionary from an external $ref.
Per swagger documentation: https://swagger.io/docs/specification/data-models/dictionaries/#:~:text=OpenAPI%20lets%20you%20define%20dictionaries,%7B, dictionaries are created via additionalProperties.

Our expectation is that when we specify additionalAttributes with named properties, the java code would generate a Map of the correct types when explicitly setting the properties. This seems to work as expected when the dictionary is defined inline to the component. However, when we include via a ref, it generates an unexpected model structure (thus breaking SerDe).

Expectation:

Main component yaml

components:
  schemas:
    Main:
      properties:
        someProperty: 
          $ref: "SomeFile.yaml#/components/schemas/SomeProperty"

SomeFile.yaml

components:
  schemas:
    SomeProperty:
      type: object
      additionalProperties:
        type: object
        properties:
          name:
            type: string
            description: Name 
          value:
            description: Value
            type: object

Expected Java Generation

public class Main {
  private Map<String, Object> someProperty;
}

Actual Java Generation

public class Main {
  private Map<String, SomeProperty> someProperty;
  ...
}

public class SomeProperty {
  private String name;
  private Object value;
 ...
}

Which obviously represents different JSON structures.

openapi-generator version

6.5.0. Yes, this is a regression.

Related issues/PRs

Similar issue, but not quite the same: https://github.com/OpenAPITools/openapi-generator/issues/14232

Suggest a fix

Should mimic behavior as if the additional properties were specified inline.

Reproduce the Spring generator case from the issue using Main and the externally referenced SomeProperty schema, focusing on additionalProperties and the external $ref path. Compare the generated Java model with the inline-schema behavior. Done means the referenced dictionary produces the expected Map<String, Object> structure without an unintended SomeProperty model.