Move validate resume step after checkout

[BDevParity]

Summary

• Moves the "Validate resume preconditions" step after the "Checkout stable branch" step so git ls-remote runs in an initialized git repo
• Fixes the failed publish crates workflow resume: https://github.com/paritytech-release/polkadot-sdk/actions/runs/23620337279/job/68797902086#step:25:20

Test plan

• Resume the publish crates workflow from the release org after this is merged and synced

[github-actions]

This pull request is amending an existing release. Please proceed with extreme caution,
as to not impact downstream teams that rely on the stability of it. Some things to consider:

• Backports are only for 'patch' or 'minor' changes. No 'major' or other breaking change.
• Should be a legit fix for some bug, not adding tons of new features.
• Must either be already audited or not need an audit.

Emergency Bypass

If you really need to bypass this check: add validate: false to each crate
in the Prdoc where a breaking change is introduced. This will release a new major
version of that crate and all its reverse dependencies and basically break the release.