"GitProtocolError: unexpected http resp 403" for a bunch of Bitbucket repos

Sentry Issue: SWH-LOADER-GIT-148

GitProtocolError: unexpected http resp 403 for https://bitbucket.org/xzyx5023515158664014333/103f8345-f88c-11e7-90ca-a0999b05dbcd.git/info/refs?service=git-upload-pack
(1 additional frame(s) were not displayed)
...
  File "swh/loader/git/loader.py", line 320, in fetch_data
    self.origin.url, base_repo, do_progress
  File "swh/loader/git/loader.py", line 242, in fetch_pack_from_origin
    progress=do_activity,
  File "dulwich/client.py", line 2080, in fetch_pack
    b"git-upload-pack", url
  File "dulwich/client.py", line 1938, in _discover_references
    resp, read = self._http_request(url, headers)
  File "dulwich/client.py", line 2224, in _http_request
    "unexpected http resp %d for %s" % (resp.status, url)

Loading failure, updating to `failed` status