Update actions/checkout action to v6 (#22)

Author: renovate[bot]

.github/workflows/lint.yaml

@@ -15,7 +15,7 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       - name: Checkout code
-        uses: actions/checkout@v5
+        uses: actions/checkout@v6
       - name: Update Shellcheck
         run: |
           sudo apt install xz-utils
@@ -31,7 +31,7 @@ jobs:
 
     steps:
       - name: Checkout code
-        uses: actions/checkout@v5
+        uses: actions/checkout@v6
 
       - name: Install shfmt
         run: brew install shfmt