[BUG] [Php] Incorrect response type handling for oneOf strategy

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?
• What's the actual output vs expected output?
• [Optional] Sponsorship to speed up the bug fix or feature request (example)

Description

openapi-generator version

5.4.0

OpenAPI declaration file content

"inputFieldDependencies": {
    "type": "array",
    "description": "",
    "items": {
        "oneOf": [
            {
                "$ref": "#/components/schemas/SingleFieldDependency"
            },
            {
                "$ref": "#/components/schemas/ConditionalSingleFieldDependency"
            }
        ]
    }
}

Generation Details

generate -i *.json -g php -o /dir --skip-validate-spec

Output

protected static $openAPITypes = [
        'input_field_dependencies' => 'OneOfSingleFieldDependencyConditionalSingleFieldDependency[]',
    ];
        /**
     * Gets input_field_dependencies
     *
     * @return OneOfSingleFieldDependencyConditionalSingleFieldDependency[]|null
     */
    public function getInputFieldDependencies()
    {
        return $this->container['input_field_dependencies'];
    }

    /**
     * Sets input_field_dependencies
     *
     * @param OneOfSingleFieldDependencyConditionalSingleFieldDependency[]|null $input_field_dependencies A list of dependencies between the input fields. These configure when the input fields should be visible.
     *
     * @return self
     */
    public function setInputFieldDependencies($input_field_dependencies)
    {
        $this->container['input_field_dependencies'] = $input_field_dependencies;

        return $this;
    }

Suggest a fix

Create oneOf strategy for php

Start with the generate -i *.json -g php command and the supplied inputFieldDependencies schema containing a oneOf array. Inspect how the PHP generator derives the displayed response type, then compare generated output with the intended separate oneOf handling; done means the generated PHP types and accessors represent the schema correctly.