test/ring-leak: get rid of warning on unchecked read

ring-leak.c: In function ‘test_iowq_request_cancel’:
ring-leak.c:131:2: warning: ignoring return value of ‘read’ declared with attribute ‘warn_unused_result’ [-Wunused-result]
  131 |  read(fds[0], buffer, 10);
      |  ^~~~~~~~~~~~~~~~~~~~~~~~

We really don't care, but the warning is annoying. So get rid of it.

Signed-off-by: Jens Axboe <axboe@kernel.dk>