Move node-update-v8-canary to GitHub Actions

[mmarchini]

With GitHub Actions there's no reason to keep the update script on Jenkins, we can move it here making it easier for folks without Jenkins admin access to help improve it when something breaks.

[targos]

Good idea. I can have a try at it.

[mmarchini]

I think this will work better if we decide to move forward with #170, but it could be implemented in the current system as well (we would just need to make sure we also cherry-pick the commit adding the Action to this repository when updating V8)

[targos]

This is live: https://github.com/nodejs/node-v8/actions/runs/737865140