CI: update cargo-check-external-types toolchain

Author: chifflier

.github/workflows/rust.yml

@@ -7,6 +7,10 @@ on:
  schedule:
  - cron: '0 18 * * *'
 
+env:
+ check_ext_rust_version: nightly-2024-06-30
+ # ^ sync with https://github.com/awslabs/cargo-check-external-types/blob/main/rust-toolchain.toml
+
 jobs:
  check:
  name: Check
@@ -91,7 +95,6 @@ jobs:
  - name: Install rust toolchain
  uses: dtolnay/rust-toolchain@master
  with:
- toolchain: nightly-2024-05-01
- # ^ sync with https://github.com/awslabs/cargo-check-external-types/blob/main/rust-toolchain.toml
- - run: cargo install cargo-check-external-types
+ toolchain: ${{ env.check_ext_rust_version }}
+ - run: cargo install --locked cargo-check-external-types
  - run: cargo check-external-types