Update actions/checkout@v5 -> v6

Author: dtolnay

.github/workflows/ci.yml

@@ -24,7 +24,7 @@ jobs:
             rust: 1.0.0
     timeout-minutes: 45
     steps:
-      - uses: actions/checkout@v5
+      - uses: actions/checkout@v6
       - uses: ./
         name: Run dtolnay/rust-toolchain${{contains(matrix.rust, ' ') && ' for ' || '@'}}${{matrix.rust}}
         id: toolchain

README.md

@@ -16,7 +16,7 @@ jobs:
     name: cargo test
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/checkout@v5
+      - uses: actions/checkout@v6
       - uses: dtolnay/rust-toolchain@stable
       - run: cargo test --all-features
 ```