Resume releases after workflow-only changes

[Stephen Belanger (Qard)]

Summary

• allow an interrupted marketplace release to resume after workflow-only commits advance main
• require the current plugin tree to be byte-for-byte identical to the existing release tag before resuming
• continue refusing to move an existing tag or deploy changed plugin content under an existing version

Root cause

The Codex v1.0.0-codex tag correctly points to the original release commit. Landing the resumability/toolchain fix advanced main, so the first retry guard would reject the existing tag even though src/plugins/codex is unchanged.

Validation

• verified src/plugins/codex is unchanged between v1.0.0-codex and current main
• go run github.com/rhysd/actionlint/cmd/actionlint@v1.7.7 .github/workflows/_release.yml
• parsed the workflow with Ruby Psych
• git diff --check