Tagging suggestion: have v4 always point to the latest v4.x.y tag

I ran into an issue yesterday because I was expecting `uses: enthought/setup-edm-action@v4` to automatically pick up the latest v4 version of the action. It turned out that I had to specify `@v4.1` explicitly to get the 4.1 version.

It looks as though what "official" actions like `checkout` do is to tag releases with `v4.minor.micro` and then recreate the `v4` tag every time there's a release to point to the latest release: https://github.com/actions/checkout/tags. We could do the same here.

(It would probably make sense to have `v4` be a lightweight tag rather than an annotated tag, but to use annotated tags for the releases as normal.)