show: fix crash with checkoutAssert

[rhubert]

Fix a regression of 0c40313b:

 File "pym/bob/cmds/show.py", line 54, in <listcomp>
   { k:v for k,v in a.getProperties().items() if not k.startswith("__") }
                    ^^^^^^^^^^^^^^^

AttributeError: 'dict' object has no attribute 'getProperties'

and add a test for this.

[jkloetzke]

Thanks.