Downgrade Node for Slither

[frangio]

The Slither check is currently randomly failing, but it seems caused by Hardhat, and allegedly downgrading Node.js should fix it.

• Failing with FileNotFoundError: [Errno 2] No such file or directory: '/github/workspace/artifacts/build-info' crytic/slither-action#56
• hardhat compile randomly and quietly stops before compiling contracts NomicFoundation/hardhat#3877

[changeset-bot]

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