Fix typo in property-hooks.xml (#4676)

Co-authored-by: Luffy <[email protected]>

Author: beesofts

language/oop5/property-hooks.xml

@@ -104,7 +104,7 @@ print $example->foo;
   </simpara>
   <simpara>
    At least one of the hooks references <code>$this->foo</code>, the property itself.
-   That means the property wll be "backed."
+   That means the property will be "backed".
    When calling <code>$example->foo = 'changed'</code>,
    the provided string will be first cast to lowercase, then saved to the backing value.
    When reading from the property, the previously saved value may conditionally be appended