fix(actions): do not require a cached state for disk regeneration

[gustavovalverde]

Motivation

Some tests, but mainly the one that create a cached state from scratch (or regenerate one), do not required an existing disk image to exists in GCP.

This also makes our weekly scheduled full sync to fail: https://github.com/ZcashFoundation/zebra/actions/runs/11179660535

Solution

• Skip the job that search for the cached disk images, as this one fails if no disk is found

Tests

• This manually triggered workflow should run the test. The test finalization is not required: https://github.com/ZcashFoundation/zebra/actions/runs/11180441616

Follow-up Work

• ref(actions): allow more flexibility on cached states usage #8908

PR Author's Checklist

• The PR name will make sense to users.
• The PR provides a CHANGELOG summary.
• The solution is tested.
• The documentation is up to date.
• The PR has a priority label.

PR Reviewer's Checklist

• The PR Author's checklist is complete.
• The PR resolves the issue.