tests: accept a test output change in [tests/test-serve.t]

This fixes a breakage introduced in adecb1ab4a0d.
It was not caught by the CI probably because allows
binding to port 13.

tests/test-serve.t

@@ -55,7 +55,7 b' With -v and -p daytime'
 #if no-windows
   $ KILLQUIETLY=Y
   $ hgserve -p daytime
-  abort: cannot start server at 'localhost:13': Permission denied (?)
+  abort: cannot start server at 'localhost:13': $EACCES$ (?)
   abort: child process failed to start (?)
   abort: no port number associated with service 'daytime' (?)
   listening at http://localhost/ (bound to $LOCALIP:13) (?)