fix: use block release validation command

[intel352]

Follow-up for GoCodeAlone/workflow#760.

Fixes the release workflow YAML quoting introduced while hardening tag handling:

• converts the pre-build validate-contract command to a block run step
• keeps the shell-level quotes around github.ref_name

Verification:

• git diff --check

[Copilot]

Pull request overview

This PR fixes YAML/shell quoting in the release workflow by converting the pre-build wfctl plugin validate-contract invocation into a block run step while preserving shell-level quoting around github.ref_name.

Changes:

• Replace the single-line run: string (which had broken nested quoting) with a multi-line run: | block for the pre-build contract validation step.
• Keep "${{ github.ref_name }}" quoted at the shell level to preserve hardening against tag edge cases.

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