Scope draft-release trigger to bundled-binary.sha256

[kitsuyui]

Summary

The prepare-draft-release workflow triggered on any push to main that touched action.yml. However, action.yml contains both the bundled binary version (version=v0.2.1) and three uses: SHA pins updated regularly by Renovate (actions/checkout, gitignore-in/install-gibo, peter-evans/create-pull-request). Each Renovate SHA-pin merge created a spurious draft release unrelated to a binary version bump.

Change

Change the push trigger path from action.yml to bundled-binary.sha256. The bundled-binary.sha256 file is only updated by prepare-release-update.yml when a new binary version is published, making it a precise semantic trigger for "bundled binary changed."

Renovate does not touch bundled-binary.sha256, so SHA-pin updates to action.yml no longer trigger draft release creation. Manual releases remain available via workflow_dispatch.

Verification

• actionlint and shellcheck: pass
• workflow_dispatch trigger is unchanged — manual releases work as before