Update actions/checkout action to v4.3.0

Author: renovate[bot]

.github/workflows/diffy.yml

@@ -11,7 +11,7 @@ jobs:
     name: Shellcheck
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/checkout@v4.2.2
+      - uses: actions/checkout@v4.3.0
       - name: Run ShellCheck
         uses: ludeeus/action-shellcheck@master