Using pytest fixture doesn't update calls with request/response on passthru

### Describe the bug

Calls not updated when using version 0.5.1 of pytest-responses.

### Additional context

The workaround for this is to not use the pytest fixture. Works perfectly when using responses module directly using PassthroughResponse.

### Version of `responses`

0.25.6

### Steps to Reproduce

```python
import requests
def test_toy_example(responses):
responses.add_passthru(re.compile("https://api.weatherstack.com/\\w+"))
response = requests.get("https://api.weatherstack.com/historical")
assert response.status_code == 200 # assertion passes
responses.calls[0].response() # index out of bounds

```

### Expected Result

Expect the calls to be populated and updated for passthrus.

### Actual Result

responses.calls are not updated/captured for passthru