chore: downgrade to `hermetic_cc_toolchain@3.1.0`

When using `3.1.1` and Bazel `8.0.0rc4` the toolchains do not get registered.

This is due to an upstream [issue] that was resolved with a [PR] to disable the
default registration in this [commit].

To upgrade past `3.1.0`, we will need to register specific toolchains.

[issue]: https://github.com/uber/hermetic_cc_toolchain/issues/181
[pr]: https://github.com/uber/hermetic_cc_toolchain/pull/190
[commit]: https://github.com/uber/hermetic_cc_toolchain/commit/f8c17de30fbf185cc5c2f61b2b508aa3b3d294a1