Don't try to parse the response json when not_modified

In case of not_modified (HTTP 304), there is no json in the response
body. Json parsing fails like:

```python
        if response.status_code == requests.codes.not_modified:
            if kwargs.get("ignore", False):
                return

        body = response
>       raise APIError(body["cause"], response=response, explanation=body)
E       TypeError: 'APIResponse' object is not subscriptable

.venv/lib/python3.12/site-packages/podman/domain/containers.py:477: TypeError
```

This patch fixes this in the way that APIError is rised with content
from the text of the requests response

Signed-off-by: Jaroslav Henner <[email protected]>

Author: jarovo

podman/domain/containers.py

@@ -472,6 +472,8 @@ def stop(self, **kwargs) -> None:
         if response.status_code == requests.codes.not_modified:
             if kwargs.get("ignore", False):
                 return
+            else:
+                raise APIError(response.text, response=response, explanation="Container already stopped.")
 
         body = response.json()
         raise APIError(body["cause"], response=response, explanation=body["message"])