Validate content_type of attachments when passed

[Kani999]

• Fixes pynetbox api calls
• Example:

  attachemnt = netbox.plugins.netbox_attachments.netbox_attachments.get(id=1)
  attachemnt .name = "asdasd"
  attachemnt .save()

• Result:
• KeyError: 'object_id'

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Check content_type and object_id when it's passed as data.