A deep dive into the wild world of GitHub Actions' tagging formats

Last week, I was tagged in a LinkedIn post, where one of the Python Core developers was noting that Astral's setup-uv GitHub Action was not being updated by either Renovate or Dependabot, and a note to users that they would need to manually update. I was a bit surprised about this - as it was the first time I'd heard about it - and this is never the scenario I'd want Renovate users to be in - manual bumping a version in a file should be a thing of the past! After digging into a GitHub Issue about this on setup-uv, it was confirmed that was due to their move from mutable GitHub Actions releases to Immutable Releases, and that Renovate wasn't handling this upgrade in a reasonable way. I had a bit of time on my hands, and some unfounded hubris for the time of day, so I thought "huh, how hard could this be?", and felt that a speedy fix would be a positive for Renovate and our users. It turns out the way that the way that tagging formats work with GitHub Actions is a little bit more…