django/backends: Improve expired token handling
I stumbled across that behavior when testing bearer tokens expiration
from swh-web
API tokens Web UI (swh-web!526 (closed)).
The first time a user sends an expired token previously used to
perform authenticated Web API calls, Keycloak will return the
following error message: "Offline session not active".
Keycloak will then remove the offline session from its database
and future calls to a Web API with the expired token will
return the following error message: "Offline user session not found"
.
So handle that error message too for indicating a token has expired.
Related to swh-web#3121 (closed)
Migrated from D5446 (view on Phabricator)