Nightly build-repro job is failing because of ed25519 compatibility

The build-repro job is failing:

  Downloaded ed25519 v1.4.0
error: failed to parse manifest at `/usr/local/cargo/registry/src/github.com-1ecc6299db9ec823/ed25519-1.4.0/Cargo.toml`
Caused by:
  feature `edition2021` is required

As near as I can tell, this is happening because our Cargo.lock now includes ed25519 version 1.4.0, which uses edition2021, which wasn't supported until Rust 1.56. Our reproducible build tools, on the other hand, use Rust 1.54.

I propose that we upgrade our reproducible-build tools to the latest Rust (1.59).

As a side-note, do we care if our Cargo.lock file requires a newer rust than our MSRV? I say "no", but we should open another ticket to discuss if so.