chore(workflows): allow dry-run release

[bendrucker]

What does this PR do?

Allows releasers to trigger a dry-run and not actually push any of the release content.

Motivation

We are getting unexpected output when generating the release content/version and need to be able to debug this without creating live releases every time.

https://github.com/observeinc/terraform-aws-lambda/actions/runs/4326680129/jobs/7554389442#step:3:89

Limitations

This can't be readily tested until it lands in main, because Actions won't process the workflow:

https://stackoverflow.com/questions/63362126/github-actions-how-to-run-a-workflow-created-on-a-non-master-branch-from-the-wo

You can dispatch on non-main branches, but the workflow content will be from the main branch:

gh workflow run 34990775 --ref test-push-false --field push=false

could not create workflow dispatch event: HTTP 422: Unexpected inputs provided: ["push"] (https://api.github.com/repos/observeinc/terraform-aws-lambda/actions/workflows/34990775/dispatches)

I've left behind @release-push in the workflow reference but this needs to be reverted as soon as we've verified that the push inputs works and can merge observeinc/.github#62.