deprecated call warnings in sync-images action output

Usually those warnings are not harmful, but it's visible to user interactions as follows:

Aug 13 01:46:23 + juju run-action --wait glance-simplestreams-sync/leader sync-images
Aug 13 01:47:31 unit-glance-simplestreams-sync-0:
Aug 13 01:47:31 UnitId: glance-simplestreams-sync/0
Aug 13 01:47:31 id: "4"
Aug 13 01:47:31 results:
Aug 13 01:47:31 Stderr: |
Aug 13 01:47:31 /usr/share/glance-simplestreams-sync/glance_simplestreams_sync.py:119: YAMLLoadWarning: calling yaml.load() without Loader=... is deprecated, as the default Loader is unsafe. Please read https://msg.pyyaml.org/load for full details.
Aug 13 01:47:31 confobj = yaml.load(f)
Aug 13 01:47:31 /usr/lib/python3/dist-packages/keystoneauth1/adapter.py:235: UserWarning: Using keystoneclient sessions has been deprecated. Please update your software to use keystoneauth1.
Aug 13 01:47:31 warnings.warn('Using keystoneclient sessions has been deprecated. '
Aug 13 01:47:31 Stdout: |
Aug 13 01:47:31 created 25015e73-4e63-4f75-8107-d9a9c10284aa: auto-sync/ubuntu-focal-20.04-amd64-server-20210720-disk1.img
Aug 13 01:47:31 status: completed
Aug 13 01:47:31 timing:
Aug 13 01:47:31 completed: 2021-08-13 01:47:30 +0000 UTC
Aug 13 01:47:31 enqueued: 2021-08-13 01:46:24 +0000 UTC
Aug 13 01:47:31 started: 2021-08-13 01:46:25 +0000 UTC