Fix republish docker branch

[damccorm]

This workflow was failing because it doesn't auto-pick up the defaults if triggered via schedule, it only uses the defaults for workflow dispatch. This meant the release/rc variables weren't getting set.

This fixes the problem and gets checkout running correctly (example). There is a good chance the workflow will still fail because all of our docker tasks are currently flaky due to #33425 but the core workflow logic should be good

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[damccorm]

R: @claudevdm

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