devel/ruby-async: update to 2.8.1

2.7.0 (2024-01-02)

What's Changed

* Try testing on Ruby 3.3. by @ioquatix in #294
* Add support for IO#timeout in io_read, io_write and io_wait. by @ioquatix
  in #296

2.8.0 (2024-01-03)

What's Changed

* Allow Interrupt to retry the run loop after issuing #stop. by @ioquatix in
  #297
* Add write timeout test. by @ioquatix in #298

2.8.1 (2024-02-01)

What's Changed

* Don't enable io_write hook on Ruby < 3.3.1 as it's buggy. by @ioquatix in
  #303

(taca)