Commit updates the build-docker workflow to add suport for ARM64 images.
Testing
=======
Locally, I attempted to build an image from the provided Dockerfile in an
ARM64 host using:
```sh
podman build -t yarr:latest -f etc/dockerfile .
```
The `platforms` input is provided as documented in [1].
1 - https://github.com/docker/build-push-action?tab=readme-ov-file#inputs
Signed-off-by: Jason Rogena <null+git@rogena.me>