CI: update toolchain version for check-external-types

Author: chifflier

.github/workflows/rust.yml

@@ -8,7 +8,7 @@ on:
  - cron: '0 18 * * *'
 
 env:
- check_ext_rust_version: nightly-2024-06-30
+ check_ext_rust_version: nightly-2025-05-04
  # ^ sync with https://github.com/awslabs/cargo-check-external-types/blob/main/rust-toolchain.toml
 
 jobs:
@@ -89,7 +89,7 @@ jobs:
  check-external-types:
  name: Validate external types appearing in public API
  runs-on: ubuntu-latest
- continue-on-error: true
+ continue-on-error: false
  steps:
  - name: Checkout sources
  uses: actions/checkout@v4