Stabilize Node 18 CI by restoring execute bit on cached Hardhat solc binaries

[Copilot]

build (18.x) was failing in GitHub Actions when Hardhat attempted to spawn a cached native compiler with EACCES. This PR hardens the Node.js CI workflow against cache permission drift in ~/.cache/hardhat-nodejs.

• Root cause addressed

  • Hardhat’s cached Linux solc binaries can be present without executable permissions, causing npm run test to fail at compiler spawn time.

• Workflow change

  • Added a focused permission-normalization step immediately after dependency install in .github/workflows/node.js.yml.
  • The step is no-op-safe when the cache path is absent.

• Implementation detail

  - name: Fix Hardhat solc permissions
    run: find ~/.cache/hardhat-nodejs/compilers-v2/linux-amd64 -type f -name "solc-linux-amd64-*" -exec chmod +x {} + || true