Can't order "xmlns" attribute

[antoine-nedelec]

Q	A
Bug report?	yes

Steps required to reproduce the problem

1. Add 2 attributes in a model, one of those attribute named xmlns, the other one doesn't matter the name

    /**
     * @var string
     * @SerializedName("xmlns")
     * @Groups({"xml_import"})
     * @XmlAttribute
     */
    private string $xmlns = 'string';

2. Try to order those attributes with @AccessorOrder
3. Check that any any case, xmlns is always at first place

Expected Result

• Attribute should be in order specified in the @AccessorOrder (or in the order they are defined in the Model if no AccessorOrder).

Actual Result

• xmlns is always rendered in first place.
• Even though xmlns is a XmlNamespace, we should be able to position it where we want ?