ceilometer-upgrade action fails with a Keystone error

Description
===============================
When running ceilometer-update on ceilometer/leader,
action fails with error:

"ERROR ceilometer The Keystone service is temporarily unavailable."

Versions
===============================
Cloud focal-victoria
Charm ceilometer rev: 278

Steps to reproduce
===============================
1. Deploy a focal-victoria bundle (i.e. openstack-on-lxd bundle https://pastebin.ubuntu.com/p/pW2NGJYG2x/ )

2. Ceilometer unit is in "blocked" state with message:
"Run the ceilometer-upgrade action on the leader to initialize ceilometer and gnocchi"

3. Run ceilomer-upgrade action with:
"juju run-action ceilometer/0 ceilometer-upgrade --wait"

4. Action fail with the error: https://pastebin.ubuntu.com/p/PjnzssXTXf/

But keystone is working correctly:
$ openstack endpoint list | grep keystone
| 32ed53350d2d4e719e03f615b3ba2c3d | RegionOne | keystone | identity | True | public | https://10.0.8.96:5000/v3 |
| b42ddcfe21df4c0998b6965b4013994c | RegionOne | keystone | identity | True | internal | https://10.0.8.96:5000/v3 |
| c75b63ec49a84c45a131afe699291a08 | RegionOne | keystone | identity | True | admin | https://10.0.8.96:35357/v3 |

$ openstack token issue
+------------+-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| Field | Value |
+------------+-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| expires | 2020-12-03T10:51:40+0000 |
| id | gAAAAABfyLUsbBdlmnDpuP8kHib-7-GM_oDo2KXAvxwKrpvW00flsytT48lEd73dOJO34zC2AYqdMZcCuH_BoCia6xkpWsMiS35SOooi9UleeTRi0sIW5QZowyLreiHPmg_jpMiF50dWCLE32yNXFjLevqs7bzkb94vJat2cIsoFM3RVBnhujFU |
| project_id | 5c19cc143cb746b6a9e765adcd9f7595 |
| user_id | 4434a217512a4bb8aa569e8f68a48ae8 |
+------------+-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+

Expected result
===============================
ceilometer-upgrade action complete and the unit is "active" state.