Charm fails to spawn openstack runners because it requests a non-existent image

[amc94]

Bug Description

The runner deployed with github-runner-image-builder will be running fine and then lose the ability to create openstack servers. The image has been pruned by the image builder and no longer exists

To Reproduce

Let the runner for a while

Environment

Juju on openstack, more specifically ps5

Relevant log output

unit-openstack-runner-9: 13:27:38 ERROR unit.openstack-runner/9.juju-log Failed to spawn a runner.
multiprocessing.pool.RemoteTraceback: 
"""
Traceback (most recent call last):
  File "/var/lib/juju/agents/unit-openstack-runner-9/charm/venv/github_runner_manager/openstack_cloud/openstack_cloud.py", line 227, in launch_instance
    server = conn.create_server(
  File "/var/lib/juju/agents/unit-openstack-runner-9/charm/venv/decorator.py", line 232, in fun
    return caller(func, *(extras + args), **kw)
  File "/var/lib/juju/agents/unit-openstack-runner-9/charm/venv/openstack/cloud/_utils.py", line 224, in func_wrapper
    return func(*args, **kwargs)
  File "/var/lib/juju/agents/unit-openstack-runner-9/charm/venv/openstack/cloud/_compute.py", line 960, in create_server
    raise exc.OpenStackCloudException(
openstack.exceptions.SDKException: Image 8891b50f-728b-43f7-8293-dfb7777fce85 was requested but was not found on the cloud

The above exception was the direct cause of the following exception:

Traceback (most recent call last):
  File "/var/lib/juju/agents/unit-openstack-runner-9/charm/venv/github_runner_manager/openstack_cloud/openstack_runner_manager.py", line 204, in create_runner
    instance = self._openstack_cloud.launch_instance(
  File "/var/lib/juju/agents/unit-openstack-runner-9/charm/venv/github_runner_manager/openstack_cloud/openstack_cloud.py", line 138, in exception_handling_wrapper
    return func(*args, **kwargs)
  File "/var/lib/juju/agents/unit-openstack-runner-9/charm/venv/github_runner_manager/openstack_cloud/openstack_cloud.py", line 250, in launch_instance
    raise OpenStackError(f"Failed to create openstack server {full_name}") from err
github_runner_manager.errors.OpenStackError: Failed to create openstack server openstack-runner-9-08f9e42eb15c

The above exception was the direct cause of the following exception:

Traceback (most recent call last):
  File "/usr/lib/python3.10/multiprocessing/pool.py", line 125, in worker
    result = (True, func(*args, **kwds))
  File "/var/lib/juju/agents/unit-openstack-runner-9/charm/venv/github_runner_manager/manager/runner_manager.py", line 404, in _create_runner
    return args.cloud_runner_manager.create_runner(registration_token=args.registration_token)
  File "/var/lib/juju/agents/unit-openstack-runner-9/charm/venv/github_runner_manager/openstack_cloud/openstack_runner_manager.py", line 212, in create_runner
    raise RunnerCreateError(f"Failed to create {instance_name} openstack runner") from err
github_runner_manager.errors.RunnerCreateError: Failed to create openstack-runner-9-08f9e42eb15c openstack runner
"""

The above exception was the direct cause of the following exception:

Traceback (most recent call last):
  File "/var/lib/juju/agents/unit-openstack-runner-9/charm/venv/github_runner_manager/manager/runner_manager.py", line 306, in _spawn_runners_using_multiprocessing
    instance_id = next(jobs)
  File "/usr/lib/python3.10/multiprocessing/pool.py", line 873, in next
    raise value
github_runner_manager.errors.RunnerCreateError: Failed to create openstack-runner-9-08f9e42eb15c openstack runner

Additional context