Update actions/checkout action to v6

Author: renovate[bot]

.github/workflows/ci.yaml

@@ -6,14 +6,14 @@ jobs:
     name: cargo test
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/checkout@v4
+      - uses: actions/checkout@v6
       - uses: dtolnay/rust-toolchain@stable
       - run: cargo test --all-features
   clippy:
     name: cargo clippy
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/checkout@v4
+      - uses: actions/checkout@v6
       - uses: dtolnay/rust-toolchain@stable
         with:
           components: clippy

.github/workflows/formatting.yaml

@@ -6,7 +6,7 @@ jobs:
     name: cargo test
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/checkout@v4
+      - uses: actions/checkout@v6
       - uses: dtolnay/rust-toolchain@stable
         with:
           components: rustfmt