Bug: ghcr images are lacking arm64

# Describe the bug

The images provided in ghcr.io/foxcpp/maddy seem to lack arm64.

# Steps to reproduce

1. Try to pull Maddy on arm64 host from ghcr.io.
2. See it fail due to manifest not including anything other than amd64

# Log files

```
docker pull ghcr.io/foxcpp/maddy:0.8.1
0.8.1: Pulling from foxcpp/maddy
no matching manifest for linux/arm64/v8 in the manifest list entries
```

The issue names ghcr.io/foxcpp/maddy and the 0.8.1 image, but no repository file or test. Start by locating the configuration or workflow that publishes the image and reproduce the pull on an arm64 host. Done means the manifest for the published image includes a linux/arm64/v8 entry.

Written by the indexing model from the issue text.