ci deploys non-`main` branches to gh-pages

[nickofthyme]

CI deploys gh-pages for non-master branches. See https://github.com/elastic/elastic-charts/actions/runs/3440483683

[markov00]

So this is a good or bad thing? Is bad because it overwrite the existing pages but good because we can also use gh pages to deploy the PR storybook?

[nickofthyme]

Yes, bad. It deploys all branches/PR to firebase but for gh-pages it should only deploy master or it will override the actual master.

The example run above was from the webGL backport on 50.2.x which replaced latest master on gh-pages as the tooltip changes are gone!

[nickofthyme]

The issue here was that the skip option for each step is determined based on changed files which does not apply to push events, only pull requests. So I added logic to override the skip and force the checks to run for upstream base branches. This forced the gh-pages deploy step to fire, causing this issue.