Ensure HTTPError.response is not None

The implementation of `HTTPError` in `requests` does not guarantee that
the `response` property will always be set. So we need to ensure it is
not `None` before looking for the return code, for example.

This also makes mypy checks pass again, as `types-request` was updated
in 2.31.0.9 to better match this particular aspect. See:
https://github.com/python/typeshed/pull/10875

swh/lister/bitbucket/lister.py

@@ -125,7 +125,7 @@ class BitbucketLister(Lister[BitbucketListerState, List[Dict[str, Any]]]):
                 body = self.http_request(self.url, params=self.url_params).json()
                 yield body["values"]
             except HTTPError as e:
-                if e.response.status_code == 500:
+                if e.response is not None and e.response.status_code == 500:
                     logger.warning(
                         "URL %s is buggy (error 500), skip it and get next page.",
                         e.response.url,