CI: switch Alpine from latest stable to Edge (MR 30)

We use this in pmbootstrap, and it is currently necessary to use Ruff.
Issue about moving Ruff to community:
https://gitlab.alpinelinux.org/alpine/aports/-/issues/15693

.gitlab-ci.yml

 ---
-image: alpine:latest
+image: alpine:edge
 
 flake8:
   before_script: