Update actions/checkout action to v6

Author: renovate[bot]

.github/workflows/ci.yaml

@@ -7,7 +7,7 @@ jobs:
     name: Lint
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/checkout@v5
+      - uses: actions/checkout@v6
       - uses: oven-sh/setup-bun@v2
         with:
           bun-version: latest
@@ -18,7 +18,7 @@ jobs:
     name: Up-to-date scripts/docs
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/checkout@v5
+      - uses: actions/checkout@v6
       - uses: oven-sh/setup-bun@v2
         with:
           bun-version: latest