Diun can't create docker client when current user does not exist.

[s17t]

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I've found a bug and checked that ...

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Description

When running diun as systemd service using diun user with home /dev/null the scheduled task will fails to check the images version against the registry.

WRN Error seeking Docker credentials error="reading registries.conf.d: lstat /dev/null/.config/containers/registries.conf.d: not a directory" image=xxx/xxx
[a line as abover for each image]
WRN Cannot get remote manifest error="cannot get image digest from HEAD request: failed to create client: stat /dev/null/.config/containers/certs.d/docker.io: not a directory"
INF Jobs completed added=0 failed=1 skipped=X unchanged=0 updated=0

Expected behaviour

It should not fails where the default registry locations does not exists or are unreadable.

Actual behaviour

Diun does not load image in its internal database.

Steps to reproduce

1. Install diun as service (i.e. systemd)
2. Run it with a user whom home is a not existent folder (i.e. /dev/null or /bin/false)

Diun version

v4.28.0

Docker info

Version:    27.3.1
 Context:    default
 Debug Mode: false
 Plugins:
  buildx: Docker Buildx (Docker Inc.)
    Version:  v0.17.1
    Path:     /usr/libexec/docker/cli-plugins/docker-buildx
  compose: Docker Compose (Docker Inc.)
    Version:  v2.29.7
    Path:     /usr/libexec/docker/cli-plugins/docker-compose

### Docker Compose config

_No response_

### Logs

```text
n/a

Additional info

No response

[crazy-max]

Seems to be an issue with github.com/containers/image module when creating the docker client and not directly related to Diun. I guess you will have the same issue with skopeo: https://github.com/containers/skopeo