test/socket/test_basicsocket: handle :wait_readable on read_nonblock

On some systems with slower local sockets, :wait_readable may
happen and we should wait on it to drain the socket.
This is a possible fix for https://bugs.ruby-lang.org/issues/13491

* test/socket/test_basicsocket.rb (test_read_write_nonblock):
  handle :wait_readable on read_nonblock

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@58437 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

test/socket/test_basicsocket.rb

@@ -193,6 +193,9 @@ class TestSocket_BasicSocket < Test::Unit::TestCase
         next
       when nil
         break
+      when :wait_readable
+        IO.select([ssock], nil, nil, 10) or
+          flunk 'socket did not become readable'
       else
         flunk "unexpected read_nonblock return: #{r.inspect}"
       end while true