Fortran: Async I/O - avoid unlocked unlocking [PR100352]

Fortran: Async I/O - avoid unlocked unlocking [PR100352]

Follow up to PR100352, which moved unit unlocking to st_*_done_worker to
avoid lock order reversal; however, as async_io uses a different lock,
the (unlocked locked) unit lock shall not be unlocked there.

libgfortran/ChangeLog:

	PR libgomp/100352
	* io/transfer.c (st_read_done_worker, st_write_done_worker): Add new
	arg whether to unlock unit.
	(st_read_done, st_write_done): Call it with true.
	* io/async.c (async_io): Call it with false.
	* io/io.h (st_write_done_worker, st_read_done_worker): Update prototype.