ci: fix encoding mismatch

Signed-off-by: Kentaro Hayashi <hayashi@clear-code.com>

Author: kenhys

test/plugin/test_out_irc.rb

@@ -106,7 +106,7 @@ def test_emit
       s = IRCParser.parse(socket.gets)
       m[s.class.to_sym] = s
 
-      s = IRCParser.parse(socket.gets)
+      s = IRCParser.parse(socket.gets&.force_encoding("utf-8"))
       m[s.class.to_sym] = s
 
       assert_equal ["##{CHANNEL}"], m[:join].channels