Launchpad CI job errors out on a snap error when using 'mantic' series

I'm trying a simple CI job
https://git.launchpad.net/~seb128/update-manager/tree/.launchpad.yaml

But it's failing on launchpad
https://launchpadlibrarian.net/690716120/buildlog_ci_update-manager_4d3ff13726e3e20c09be1eed82f186f30fbb9d58_BUILDING.txt.gz

```
Running linter:0
cmd_run.go:1046: WARNING: cannot create user data directory: cannot create snap home dir: mkdir /nonexistent: permission denied
Sorry, home directories outside of /home needs configuration.
See https://forum.snapcraft.io/t/11209 for details.
Job failed
Traceback (most recent call last):
  File "/usr/lib/python3/dist-packages/lpbuildd/target/run_ci.py", line 240, in run
    self.run_job()
  File "/usr/lib/python3/dist-packages/lpbuildd/target/run_ci.py", line 232, in run_job
    self.run_build_command(args, env=env)
  File "/usr/lib/python3/dist-packages/lpbuildd/target/run_ci.py", line 173, in run_build_command
    super().run_build_command(
  File "/usr/lib/python3/dist-packages/lpbuildd/target/operation.py", line 62, in run_build_command
    return self.backend.run(args, cwd=cwd, env=full_env, **kwargs)
  File "/usr/lib/python3/dist-packages/lpbuildd/target/lxd.py", line 716, in run
    subprocess.check_call(cmd, **kwargs)
  File "/usr/lib/python3.8/subprocess.py", line 364, in check_call
    raise CalledProcessError(retcode, cmd)
subprocess.CalledProcessError: Command '['lxc', 'exec', 'lp-mantic-amd64', '--env', 'LANG=C.UTF-8', '--env', 'SHELL=/bin/sh', '--env', 'http_proxy=http://10.10.10.1:8222/', '--env', 'https_proxy=http://10.10.10.1:8222/', '--env', 'GIT_PROXY_COMMAND=/usr/local/bin/lpbuildd-git-proxy', '--env', 'SNAPPY_STORE_NO_CDN=1', '--', '/bin/sh', '-c', "cd /build/tree && linux64 runuser -u buildd -g buildd -G lxd -- /bin/bash -o pipefail -c 'lpci -v run-one --output-directory /build/output linter 0 2>&1 | tee /build/output/linter/0/log'"]' returned non-zero exit status 1.
```

Locally with the 0.2.4 snap the same job is failing with a key error on 'mantic' as series. Changing to 'devel' and the job is working locally but then launchpad is not even giving it a try as showed by the previous commit on https://code.launchpad.net/~seb128/update-manager/+git/update-manager/+ref/main