Upgrade checkout action in workflows to v4

> This is an automatically generated PR.

actions/checkout got a new release with v4. Shouldn't affect anything, just newer.

@rebuy-de/it-platform FYI

.github/workflows/ci.yaml

@@ -21,7 +21,7 @@ jobs:
       with:
         go-version: '1.21'
     - name: Checkout code
-      uses: actions/checkout@v3
+      uses: actions/checkout@v4
       with:
         fetch-depth: 0
     - name: Build Project