"Export DPM configuration" expects inventory-error-details to always be present

[EdGue42]

The "Export DPM configuration" operation uses the "GET inventory" operation, and assumes that any ""inventory-error" objects always contain the "inventory-error-details" field. But according to the WSAPI spec, this field is only present if "inventory-error-code" is 5.

This leads to errors such as:

  File "/Users/guenthne/github/ibm/my-machine/config/dot-virtualenvs/zhmccli/lib/python3.11/site-packages/zhmcclient/_cpc.py", line 3135, in retrieveInventoryData
    f"Details: {dict(item.get('inventory-error-details'))}")
                ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
TypeError: 'NoneType' object is not iterable