Bump package version

This package is in a rolling state. There are no releases and no plans
to make them, so the `.dev` part of the version string is intended to
indicate the "in development" state of the package.
The version part `2.4` is used due to historical reasons (to be greater
than the last used version string).

Disregard the available tags, they exist only to ease the navigation
in commit history.

 from setuptools import find_packages, setup
 
-version = '2.3'
+version = '2.4.dev0'
 
 setup(name='op_robot_tests',
       version=version,