chore(deps): update actions/checkout action to v6

Author: renovate[bot]

.github/workflows/checks.yaml

@@ -9,7 +9,7 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       - name: checkout
-        uses: actions/checkout@v3
+        uses: actions/checkout@v6
 
       - name: REUSE compliance
         uses: fsfe/reuse-action@v2

.github/workflows/rust.yaml

@@ -8,15 +8,15 @@ jobs:
   build-example:
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/checkout@v3
+      - uses: actions/checkout@v6
       - uses: actions-rs/toolchain@v1
         with:
           toolchain: stable
       - run: cargo build --example echo
   clippy:
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/checkout@v3
+      - uses: actions/checkout@v6
       - run: rustup component add clippy
       - uses: actions-rs/clippy-check@v1
         with: