clnrest's `utoipa-swagger-ui` library has an indirect `rust-embed` dependency which by default includes timestamps in build. It results in non-deterministic build for clnrest. Using environment variable `SOURCE_DATE_EPOCH` with fixed value will enforce a consistent timestamp for builds.
Also adding the `--locked` flag to ensure the release build uses exact dependencies from Cargo.lock. The `--locked` flag is particularly important for deterministic builds as it prevents Cargo from updating the lockfile.
Fixes#8288.
Changelog-Fixed: Core lightning builds for Ubuntu Focal, Jammy and Noble are deterministic again.
490fb0fc3b