Pin docker version to a known stable release

auto-build-image is technically also affected by the hanging builds gitlab-org/gitlab-runner#6697 (closed), except it doesn't have much activity.

This changes the version to match what is already pinned on .com

As part of gitlab-org/configure/general#32 (closed), I want to add an item to rebuild this image, and it makes sense to base it on the same tag as the tag used in the CI YAML templates.