Deprecate SplFixedArray::__wakeup() (#9704)

GH-9354 added the `__serialize` and `__unserialize` method,
so unserialize() and other unserializers will call `__unserialize`
instead of `__wakeup` for SplFixedArray and userland subclasses.

RFC: https://wiki.php.net/rfc/deprecations_php_8_4#deprecate_splfixedarraywakeup

Author: TysonAndre

ext/spl/spl_fixedarray.stub.php

@@ -6,7 +6,10 @@ class SplFixedArray implements IteratorAggregate, ArrayAccess, Countable, JsonSe
 {
     public function __construct(int $size = 0) {}
 
-    /** @tentative-return-type */
+    /**
+     * @tentative-return-type
+     * @deprecated
+     */
     public function __wakeup(): void {}
 
     public function __serialize(): array {}