tests: Fix test failures with kombu >= 5.2.4

kombu 5.2.4 fixed an off-by-one issue that meant we were attempting
retries more than once [1]. We need to handle this to unblock the gate.
This was discovered by examining the call stack and comparing this with
recent changes in openstack/requirements.

[1] https://github.com/celery/kombu/commit/5bed2a8f983a3bf61c12443e7704ffd89991ef9a



Change-Id: I476e3c573523d5991c56b31ad4df1172196aa7f1
Signed-off-by: Stephen Finucane <sfinucan@redhat.com>