Fix Rule::enum on array items replacing array type in OpenAPI spec

[dbrekelmans]

Follow-up to #1119 (comment), applies the same fix to Rule::enum.

When Rule::enum is used on array items (e.g. ['array', Rule::enum(StatusEnum::class)]), the EnumRule transformer ignores the previous type and returns the enum type directly, discarding the array entirely.

Before (incorrect):

  {
    "$ref": "#/components/schemas/StatusEnum"
  }

After (correct):

  {
    "type": "array",
    "items": {
      "$ref": "#/components/schemas/StatusEnum"
    }
  }

Note on test skips

The only() and except() array tests use ->skip(! method_exists(Enum::class, 'only')) / ->skip(! method_exists(Enum::class, 'except')), because these methods were only added in Laravel 11. This matches the existing skip conditions on the non-array only/except tests.