Add a RunNumber with mag down to G-on-G upgrade tests

@gcorti @dpopov

This is to make sure that the magnetic field via DD4hep conditions is active and its polarity is down. The run number is in sync with what has been chosen in AppConfig: AppConfig!186 (merged)

I added the same run number to the DetDesc test just to have the random seed based on the same run number value.

assigned to @gcorti

approved this merge request

Hi @dpopov, this is needed to be able to enable the magnetic field in G-on-G. Could you please go ahead and merge it?

merged

mentioned in commit 189f2074