Defer GitHub releases until after NPM packages are published

[dgp1130]

Action item from requiem/doc/postmortem475066.

In the 14.1.0-rc.0 release, the NPM publish operation failed several times. However the GitHub release was published before NPM failed, so each attempt published a GitHub release which isn't actually usable and confuses people watching the repository. These phantom releases also need to be manually cleaned up afterwards.

We should consider deferring the GitHub release until after the NPM publish is successful. If the NPM publish does fail, we might want to print an error message that the GitHub release was not posted, but that's probably less of a concern.

[devversion]

That is an interesting point. I specifically made it run before any NPM release is cut so that it is "usually" trivial to just finish the remaining NPM publishes, but not having to e.g. manually create the tag, release entry (with changelog etc.)