Use main in versions.txt instead of Ruby version tags

Problem

The download URLs in versions.txt use Git tags in the artifact paths (e.g., /jobs/artifacts/3.2.8/raw/...). This means we have to manually create and maintain Git tags for each Ruby version. This adds manual steps and can get out of sync, but the pipeline on main already builds all the binaries on every merge.

Impact

If a tag is missing or outdated, the download for that version will fail. Maintaining tags is just extra work.

Proposal

Change the URLs in versions.txt to point to main instead of specific tags. The main pipeline already builds everything, so downloads will still work and we can skip the manual tagging.

Impacted categories

The following categories relate to this issue:

• gdk-reliability - e.g. When a GDK action fails to complete.
• gdk-usability - e.g. Improvements or suggestions around how the GDK functions.
• gdk-performance - e.g. When a GDK action is slow or times out.