release v2.2.0

No changes from RC2.
* RC2:
  * Fix PHP-8.2 compatibility (see gh issue #165)
* RC1:
  * Fix PHP-8.1 compatibility (see gh issues #161, #157, and #156)
  * Add support for ZEND_ACC_NOT_SERIALIZABLE and magic __{,un}serialize

Author: m6w6