ci: pin nightly toolchain (#112)

This PR flips the script on #92 and pins the nightly toolchain. This is
necessary due to an [upstream
issue](dalek-cryptography/curve25519-dalek#618)
that now fails nightly CI.

.github/workflows/test.yml

@@ -12,10 +12,10 @@ jobs:
  - name: toolchain
  uses: dtolnay/rust-toolchain@master
  with:
- toolchain: nightly 
+ toolchain: nightly-2024-02-01
  targets: wasm32-unknown-unknown
  - name: build (WASM)
- run: cargo +nightly build --target wasm32-unknown-unknown --no-default-features -Zavoid-dev-deps
+ run: cargo +nightly-2024-02-01 build --target wasm32-unknown-unknown --no-default-features -Zavoid-dev-deps
 
  test:
  name: cargo test
@@ -24,7 +24,7 @@ jobs:
  matrix:
  rust:
  - stable
- - nightly
+ - nightly-2024-02-01
  steps:
  - name: checkout
  uses: actions/checkout@v4