Merge pull request #577 from gruenich/feature/github-action-checkout-v4

[ci] Update actions/checkout to version 4

Author: mlschroe

.github/workflows/ci.yml

@@ -14,7 +14,7 @@ jobs:
   build:
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/checkout@v2
+      - uses: actions/checkout@v4
       - name: Setup
         run:  |
           sudo apt-get install cmake liblzma-dev