PHP - anyOf/oneOf primitive type array serialization wrong

related #5348

## Repo

```yaml
openapi: 3.0.3
info:
title: Example
description: Example
version: 1.0.0
servers:
- url: https://example.com/api
paths:
'/example1':
post:
summary: Test error generation.
description: "Test generating error with message property."
operationId: postErrorGeneration
responses:
'200':
description: Success
content:
application/json:
schema:
$ref: '#/components/schemas/Success'
components:
schemas:
Success:
type: object
oneOf:
- type: string
- type: array
items:
type: string
```

(or update to anyOf)

## deseralization

```php
public static function createFromDiscriminatorValue(ParseNode $parseNode): ItemPostRequestBody_tax_rates {
$result = new ItemPostRequestBody_tax_rates();
if ($parseNode->getStringValue() !== null) {
$result->setItemPostRequestBodyTaxRatesString($parseNode->getStringValue());
} else if ($parseNode->getCollectionOfObjectValues([string::class, 'createFromDiscriminatorValue']) !== null) {
$result->setString($parseNode->getCollectionOfObjectValues([string::class, 'createFromDiscriminatorValue']));
}
return $result;
}
````

Should instead call out getCollectionOfPrimitiveValues for the second case.

## serialization

```php
public function serialize(SerializationWriter $writer): void {
if ($this->getItemPostRequestBodyTaxRatesString() !== null) {
$writer->writeStringValue(null, $this->getItemPostRequestBodyTaxRatesString());
} else if ($this->getString() !== null) {
$writer->writeCollectionOfPrimitiveValues(null, $this->getString());
}
}

```

Should instead call writeCollectionOfPrimitiveValues for the second case, the conditions are inverted, and the property/getter `getItemPostRequestBodyTaxRatesString` should be an array of strings, not a simple string.

Use the supplied OpenAPI schema with string and string-array oneOf or anyOf branches to inspect the generated PHP createFromDiscriminatorValue and serialize methods. Trace how primitive arrays are represented and emitted, then verify that generated output uses the primitive collection methods, the correct conditions, and an array-of-strings property.

Written by the indexing model from the issue text.