sshpeer: convert command name to sysstr before accessing method

Method name are `str` so we should pass them as `str`.

mercurial/sshpeer.py

@@ -130,7 +130,7 b' class doublepipe:'
             if sideready:
                 _forwardoutput(self._ui, self._side)
             if mainready:
-                meth = getattr(self._main, methname)
+                meth = getattr(self._main, pycompat.sysstr(methname))
                 if data is None:
                     return meth()
                 else: