fix(helm): due to a bug in checkout action we need to use github.sha

[slonka]

Due to a bug in checkout action mentioned here actions/checkout#1359 and here actions/checkout#881 we need to explicitly set ref to have the proper SHA put in helm charts on pull requests builds.

Changelog: skip

Checklist prior to review

• Link to relevant issue as well as docs and UI issues --
• This will not break child repos: it doesn't hardcode values (.e.g "kumahq" as a image registry) and it will work on Windows, system specific functions like syscall.Mkfifo have equivalent implementation on the other OS --
• Tests (Unit test, E2E tests, manual test on universal and k8s) --
• Do you need to update UPGRADE.md? --
• Does it need to be backported according to the backporting policy? --
• Do you need to explicitly set a > Changelog: entry here or add a ci/ label to run fewer/more tests?

[michaelbeaumont]

I think this isn't necessarily a bug per se, we're checking out a different commit now, PR branch head vs a merge commit. I think it's what we want though and I think it matches CircleCI.