Fix traceback in on_unreachable

Fixes #10960

lib/ansible/callbacks.py

@@ -392,6 +392,7 @@ class CliRunnerCallbacks(DefaultRunnerCallbacks):
     def on_unreachable(self, host, res):
         if type(res) == dict:
             res = res.get('msg','')
+        res = to_bytes(res)
         display("%s | FAILED => %s" % (host, res), stderr=True, color='red', runner=self.runner)
         if self.options.tree:
             utils.write_tree_file(