ci: nightly rust versions in variables

.github/workflows/lint.yml

@@ -66,15 +66,15 @@ jobs:
         run: cargo +nightly doc --no-deps --workspace --all-features
 
   check-external-types:
-    if: false # disable until https://github.com/awslabs/cargo-check-external-types/pull/177 is marged
+    if: false # rustdoc mismatch currently
     runs-on: ubuntu-latest
     steps:
       - uses: actions/checkout@v4
 
-      - name: Install Rust (nightly-2024-05-01)
+      - name: Install Rust (${{ vars.RUST_VERSION_EXTERNAL_TYPES }})
         uses: actions-rust-lang/[email protected]
         with:
-          toolchain: nightly-2024-05-01
+          toolchain: ${{ vars.RUST_VERSION_EXTERNAL_TYPES }}
 
       - name: Install just
         uses: taiki-e/[email protected]
@@ -87,7 +87,7 @@ jobs:
           tool: cargo-check-external-types
 
       - name: check external types
-        run: just check-external-types-all +nightly-2024-05-01
+        run: just check-external-types-all +${{ vars.RUST_VERSION_EXTERNAL_TYPES }}
 
   public-api-diff:
     runs-on: ubuntu-latest
@@ -100,10 +100,10 @@ jobs:
       - name: Checkout PR branch
         uses: actions/checkout@v4
 
-      - name: Install Rust (nightly-2024-09-30)
+      - name: Install Rust (${{ vars.RUST_VERSION_API_DIFF }})
         uses: actions-rust-lang/[email protected]
         with:
-          toolchain: nightly-2024-09-30
+          toolchain: ${{ vars.RUST_VERSION_API_DIFF }}
 
       - name: Install cargo-public-api
         uses: taiki-e/[email protected]