When github.action_ref is not a semver tag (e.g. main), skip binary
download and run vociferate directly via 'go run ./cmd/vociferate' from
the action's own source directory (GITHUB_ACTION_PATH). A conditional
Setup Go step installs the toolchain only on that path.
When pinned to a semver tag (v*), the existing prebuilt binary download
and cache behaviour is unchanged.
This makes the prepare-release workflow self-contained on main — it no
longer requires a published release to bootstrap itself.
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