[BUG][JAVA] Validation fails when referencing schema properties in other schema

Bug Report Checklist

• Have you provided a full/minimal spec to reproduce the issue?
• Have you validated the input using an OpenAPI validator (example)?
• Have you tested with the latest master to confirm the issue still exists?
• Have you searched for related issues/PRs?

Description

When referencing properties of a schema inside a schema definition it fails to validate spec but when I skip the validation the correct code is generated

openapi-generator version

5.2.0

OpenAPI declaration file content or url

Concerned specification

Reproduction steps

I am using the npm wrapper to run the following command:
openapi-generator-cli generate -i schema.yaml --additional-properties=typescriptThreePlus=true,modelPropertyNaming=camelCase -g typescript-fetch -o outputDir

And I get this uncaught exception:

Exception in thread "main" org.openapitools.codegen.SpecValidationException: There were issues with the specificat
ion. The option can be disabled via validateSpec (Maven/Gradle) or --skip-validate-spec (CLI).
 | Error count: 3, Warning count: 0
Errors:
        -attribute paths.'/parts/{id}/'(patch).requestBody.content.'application/x-www-form-urlencoded'.schema.prop
erties is not of type `object`
        -attribute paths.'/parts/{id}/'(patch).requestBody.content.'multipart/form-data'.schema.properties is not
of type `object`
        -attribute paths.'/parts/{id}/'(patch).requestBody.content.'application/json'.schema.properties is not of
type `object`
        at org.openapitools.codegen.config.CodegenConfigurator.toContext(CodegenConfigurator.java:546)
        at org.openapitools.codegen.config.CodegenConfigurator.toClientOptInput(CodegenConfigurator.java:573)
        at org.openapitools.codegen.cmd.Generate.execute(Generate.java:433)
        at org.openapitools.codegen.cmd.OpenApiGeneratorCommand.run(OpenApiGeneratorCommand.java:32)
        at org.openapitools.codegen.OpenAPIGenerator.main(OpenAPIGenerator.java:66)

Fix

I am currently using the --skip-validate-spec to bypass this error and the correct code is generated so I guess this is a validation error

Start with the linked schema.yaml reproduction and the validation path shown in CodegenConfigurator.toContext and toClientOptInput. Run the supplied openapi-generator-cli command with validation enabled, then confirm that the referenced schema properties are accepted while typescript-fetch generation still produces the correct code.