## Description 

There seems to be a build issue with a dependency not supporting Rust
1.72 or nightly.
According to https://substrate.stackexchange.com/a/9069, we can pin the
nightly toolchain version for now until the main repo has upgraded.

## Test Plan 

https://github.com/MystenLabs/sui/actions/runs/5602870164

---
If your changes are not user-facing and not a breaking change, you can
skip the following section. Otherwise, please indicate what changed, and
then add to the Release Notes section as highlighted during the release
process.

### Type of Change (Check all that apply)

- [ ] protocol change
- [ ] user-visible impact
- [ ] breaking change for a client SDKs
- [ ] breaking change for FNs (FN binary must upgrade)
- [ ] breaking change for validators or node operators (must upgrade
binaries)
- [ ] breaking change for on-chain data layout
- [ ] necessitate either a data wipe or data migration

### Release notes