Update actions/checkout action to v6

Author: renovate[bot]

.github/workflows/build.yml

@@ -23,7 +23,7 @@ jobs:
         with:
           rust-version: ${{ matrix.rust }}
 
-      - uses: actions/checkout@v5
+      - uses: actions/checkout@v6
 
       - name: Build
         run: cargo build --verbose

.github/workflows/publish.yml

@@ -21,7 +21,7 @@ jobs:
         with:
           rust-version: ${{ matrix.rust }}
 
-      - uses: actions/checkout@v5
+      - uses: actions/checkout@v6
 
       - name: Publish
         run: cargo publish --token ${CRATES_TOKEN}