Replace `response.ok` with `response.is_success`

I have a couple of unit tests like these:
```
response = client.post(Routes.JOBS, json=job_dict)
assert response.ok
```

Based on https://www.python-httpx.org/compatibility/#checking-for-success-and-failure-responses (and https://github.com/encode/httpx/issues/543, https://github.com/encode/httpx/pull/574) a replacement for this requests functionality in httpx exists with `response.is_success`

Search the unit tests for uses of response.ok, starting with the example involving client.post(Routes.JOBS, json=job_dict). Replace those checks with response.is_success, then run the test suite to confirm the updated assertions pass.

Written by the indexing model from the issue text.