Fix terraform backend credential issue

[abikouo]

SUMMARY

When trying to sync inventory using terraform backend credentials, the job failed when the credential is not a google credential type.

  File "/awx_devel/awx/main/models/inventory.py", line 1507, in build_private_data
    return self.build_plugin_private_data(inventory_update, private_data_dir)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/awx_devel/awx/main/models/inventory.py", line 1663, in build_plugin_private_data
    gce_cred = credential.get_input('gce_credentials')
               ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/awx_devel/awx/main/models/credential/__init__.py", line 290, in get_input
    raise AttributeError(field_name)
AttributeError: gce_credentials

This issue has been introduced by the merge of #15055
This fix consists in checking whether the user as provided some google credentials.

ISSUE TYPE

• Bug, Docs Fix or other nominal change

COMPONENT NAME

• API

AWX VERSION

24.3.1.dev7+g2fbbd10b1d

ADDITIONAL INFORMATION