Skip tasks that shouldn't run on skip_deploy

[benjy44]

• Skip tasks that shouldn't run on skip_deploy
• use $(git rev-parse HEAD^) instead of github.event.before, so squashed commits that are forced-pushed work

I had opened a PR earlier that was not properly tested, but this one should be better and tested, it fixes two issues we were facing with our deployments

[benjy44]

Hi @sunkickr @iancmoritz , any chance to review this PR?

[benjy44]

I've had the same issue that made me open this PR in the first place with the latest change pushed to wake up deployments. So I added the same change for those steps, ie: skip the steps that should not run on skip_deploy (without this change, the action breaks when preview deployment is being deleted)

[benjy44]

closing this as it didn't get much interests from the maintainers and the action has changed signigicantly since my PR.
Maybe the issues I mentioned are already fixed
I can see the current action still uses git diff --name-only $GITHUB_EVENT_BEFORE $GITHUB_EVENT_AFTER so squash commits are still broken most likely