contracts-bedrock: fix slither

[tynes]

Description
Fixes slither to work in CI, this is a temp fix until we can configure the outdir for build-info using foundry, see https://app.circleci.com/pipelines/github/ethereum-optimism/optimism/3883/workflows/d23c46f9-501a-4853-9305-d12ff1a12d0b/jobs/52916/steps

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[tynes]

PR in ethers-rs to make the outdir configurable: gakonst/ethers-rs#1433
Will need follow up PRs in foundry + hh plugin which should be straight forward to implement