[CI.yaml] Bump to actions/checkout@v6.

Author: lgarron

.github/workflows/CI.yaml

@@ -9,15 +9,15 @@ jobs:
     runs-on: ubuntu-latest
 
     steps:
-      - uses: actions/checkout@v4
+      - uses: actions/checkout@v6
       - uses: oven-sh/setup-bun@v2
       - run: make setup
       - run: make lint
 
   fish:
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/checkout@v4
+      - uses: actions/checkout@v6
       - run: ls /home/runner/work/actions-workflows/actions-workflows/.github/workflows/
       - uses: ./actions/install-fish
       - run: fish --version