If tag isn't specified, fall back to publishConfig

[rikoe]

It would be great if the action can actually check if a tag is specified as part of publishConfig in package.json, otherwise whenever wanting to switch between @next or @latest for tags, I have to directly modify the github workflow file itself, which is kind of hidden away and easily forgotten.

Also, it is more correct to use the publishConfig fallback in package.json for tag, instead of hard-coding to latest if not specified in GitHub action options.