Docs: Document aria-live and hidden in safecss_filter_attr().

In [56603], support was added for `aria-live` and `hidden` attributes in `safecss_filter_attr()`.

This adds a `@since` annotation to document this change.

Follow-up to [56603].

Props mukesh27.
See #57791.

git-svn-id: https://develop.svn.wordpress.org/trunk@56608 602fd350-edb4-49c9-b593-d223f7449a82

src/wp-includes/kses.php

@@ -2631,6 +2631,7 @@ function safecss_filter_attr( $css, $deprecated = '' ) {
  * @since 5.0.0 Added support for `data-*` wildcard attributes.
  * @since 6.0.0 Added `dir`, `lang`, and `xml:lang` to global attributes.
  * @since 6.3.0 Added `aria-controls`, `aria-current`, and `aria-expanded` attributes.
+ * @since 6.4.0 Added `aria-live` and `hidden` attributes.
  *
  * @access private
  * @ignore