Update CI checkout action

Author: jlaunonen

.github/workflows/test.yml

@@ -10,7 +10,7 @@ jobs:
   Test:
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/checkout@v2
+      - uses: actions/checkout@v4
       - uses: actions/setup-python@v4
         with:
           python-version: '3.12'