Add small test for GaudiPython.Bindings.iDataSvc

While fixing some tests in LHCb's LCG_99 build I came across some problems with the GaudiPython bindings and noticed that they aren't really tested in Gaudi.

This is a tiny improvement upon that, which will hopefully show some problems with these bindings when using the new ROOT/cppyy in LCG_99

I don't quite have the time right now to tackle fixing all these bindings so figured I could at least try and create a small test triggering some of the problems I saw.

cc @clemenci