CI: use common action for cargo-check-external-types

Author: chifflier

.github/workflows/rust.yml

@@ -87,10 +87,5 @@ jobs:
     steps:
       - name: Checkout sources
         uses: actions/checkout@v5
-      - name: Install rust toolchain
-        uses: dtolnay/rust-toolchain@master
-        with:
-          toolchain: nightly-2025-08-06
-          # ^ sync with https://github.com/awslabs/cargo-check-external-types/blob/main/rust-toolchain.toml
-      - run: cargo install cargo-check-external-types
-      - run: cargo check-external-types
+      - id: cargo-rdme
+        uses: rusticata/ci-action-check-external-types@v1