Properly set RUBY_VERSION and ALPINE_VERSION in single image
In !3370 (merged), I forgot to also set the RUBY_VERSION
and ALPINE_VERSION
variables when building the Docker image. This was caught in the monthly docs release and fixed with !3392 (merged).
This MR implements the initial MR, and properly adds the variables to docker-images.gitlab-ci.yml
.
Closes #1356 (closed)