main/at-spi2-core: upgrade to 2.48.4
What's new in at-spi2-core 2.48.4:
* Add atspi_get_version() to return the runtime version of the AT-SPI library.
* collection: Fix match testing for attributes.
* collection: Avoid locking up if an object has a very large child count
* Fix possible NULL pointer dereference when deregistering an event listener.
* Various fixes for the new key grabbing API.