Upgrade Dockerfile to use Go 1.21 and Alpine 3.19
- https://github.com/gohugoio/hugo/commit/eb9f1eb657e6782cb3ed13203a58d91adf185640
- https://alpinelinux.org/posts/Alpine-3.19.0-released.html
Seems the newer Hugo versions are built with Go 1.25.1 https://github.com/gohugoio/hugo/releases/tag/v0.121.1.
Edited by Achilleas Pipinellis