[Bug]: Update nb_inventory to work with NetBox 3.5

### Ansible NetBox Collection version

v3.12.0

### Ansible version

```
ansible [core 2.13.9]
```


### NetBox version

v3.5-beta2

### Python version

3.8

### Steps to Reproduce

Use nb_inventory plugin with NetBox 3.5.

### Expected Behavior

It to present a working inventory.

### Observed Behavior

Crashes on fetching the openapi schema,