PHP Client does not handle default values correctly when they are ENUM references

The default values set in the constructor for PHP Model classes does not correctly reference self::.

I believe the offending code is this line:
https://github.com/OpenAPITools/openapi-generator/blob/d9a6f4d7261d523d933e4cd33e6abc48d4d0b5e2/modules/openapi-generator/src/main/resources/php/model_generic.mustache#L164

example generated code:

        $this->container['code'] = isset($data['code']) ? $data['code'] : CODE_200;

expected:

        $this->container['code'] = isset($data['code']) ? $data['code'] : self::CODE_200;

Start in modules/openapi-generator/src/main/resources/php/model_generic.mustache at the referenced line and inspect how default values are rendered for enum references. Generate a PHP model containing an enum default and verify that the resulting constructor uses self::CODE_200 rather than CODE_200; done means the generated default is a valid class-constant reference.