Rewrite .woodpecker.yml to use Alpine and pipx (#206)
    
    The current CI pipeline was a workaround for Codeberg-CI/feedback#117 and is currently broken. This PR makes it use Alpine and pipx instead which should be more reliable.
    
    Reviewed-on: https://codeberg.org/ForgeFed/ForgeFed/pulls/206
    Co-authored-by: Anthony Wang <a@exozy.me>
    Co-committed-by: Anthony Wang <a@exozy.me>