Need pinned SHA in the github workflow

```The actions actions/checkout@v4, dtolnay/rust-toolchain@master, actions/setup-node@v4, actions/setup-python@v5, and pre-commit/action@v3.0.1 are not allowed in braintrustdata/bt because all actions must be pinned to a full-length commit SHA.```

So the CI is currently broken and won't run.