Upgrade actions/checkout@v4

Node.js 16 actions are deprecated.
actions/checkout@v4 uses Node.js 20

Author: oh2fih

.github/workflows/black.yml

@@ -12,7 +12,7 @@ jobs:
     name: Black
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/checkout@v3
+      - uses: actions/checkout@v4
       - name: Check Black formatting for Python scripts
         uses: psf/black@stable
         with:

.github/workflows/shell.yml

@@ -12,7 +12,7 @@ jobs:
     name: ShellCheck
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/checkout@v3
+      - uses: actions/checkout@v4
       - name: Run ShellCheck for shell scripts
         uses: ludeeus/action-shellcheck@master
         with: