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
```

该 issue 提到了 ghcr.io/foxcpp/maddy 和 0.8.1 镜像，但没有指定任何仓库文件或测试。首先定位用于发布该镜像的配置或 workflow，并在 arm64 主机上复现 pull。已完成的标准是：已发布镜像的 manifest 包含一个 linux/arm64/v8 条目。

由索引模型根据 Issue 内容生成。