Update Jetpack Beta URL for latest release downloading

[oskosk]

The Jetpack Beta Tester Plugin started being developed on the Jetpack monorepo, so the former repo is no longer a valid source for getting a master copy and installing on JN

For now JN is carrying a manual change making it download

https://github.com/Automattic/jetpack-beta/releases/latest/download/jetpack-beta.zip

Update: Seems like the intention was for the jetpack-beta repository to have a full blown vendor directory but there was an oversight in the automation process that ships code form the Jetpack monorepo to the Jetpack Beta Tester repository..

Still, it may be best if Jurassic Ninja downloaded a latest release bundle instead of a master bundle so to allow developers to have unreleased work in master without compromising the latest official release of the Jetpack Beta Tester plugin

[brbrr]

This PR should resolve the issue in current master: Automattic/jetpack#20187

[kraftbj]

I'd agree that we should run latest release instead of master, by default.

It would be nice to be able to indicate master from special ops so we can smoke test before tagging a new version.

[oskosk]

It would be nice to be able to indicate master from special ops so we can smoke test before tagging a new version.

good call!