[11.x] Fixes incorrectly serializing virtual properties (backport)

src/Illuminate/Database/Eloquent/Model.php

@@ -2421,7 +2421,15 @@ public function __sleep()
         $this->classCastCache = [];
         $this->attributeCastCache = [];
 
-        return array_keys(get_object_vars($this));
+        // When serializing the model, we may accidentally catch up some virtual properties.
+        // We will cast the model to a native array to skip them and then apply a function
+        // to clean each of the property names which is miles faster than using a regex.
+        return array_map(
+            fn ($key) => $key[0] === "\0"
+                ? substr($key, strpos($key, "\0", 1) + 1)
+                : $key,
+            array_keys((array) $this)
+        );
     }
 
     /**