Harden GHAs with commit SHA

### Description

Pin GHAs for with commit SHAs[^1] for increased security and reliability.

[^1]: https://docs.github.com/en/actions/reference/security/secure-use#using-third-party-actions

### Code of Conduct

- [x] I agree to follow the [IETF's Code of Conduct](https://github.com/ietf-tools/.github/blob/main/CODE_OF_CONDUCT.md)