Fix a bug in objspace.fake.checkmodule which was introduced 5 years ago by 2acc241fc909
The call to module.init() causes module.startup() to be called at translation-time and sets module.startup_called = True. The net effect is that we freeze values which are supposed to be computed at runtime, and this e.g. causes problems to HPy.
The original commit added the call to module.init() to be able to ztranslate _multiprocessing: fix it differently by moving the relevant code to startup().
These buildots are passing: