Update to actions/checkout@v4 (#5653)

Update to [actions/checkout@v4](https://github.com/actions/checkout/releases/tag/v4.0.0)

According to actions/checkout#1448 it might fix the issue we are encountering. Even if it doesn't, no apparent harm from using the latest version.

.github/workflows/main.yml

@@ -23,7 +23,7 @@ jobs:
       BALTO_TOKEN: ${{ secrets.BALTO_TOKEN }}
 
     steps:
-    - uses: actions/checkout@v3
+    - uses: actions/checkout@v4
     - run: git fetch --prune --unshallow
     - name: construct container name
       run: |
@@ -79,7 +79,7 @@ jobs:
     name: Check formatting
     runs-on: ubuntu-latest
     steps:
-    - uses: actions/checkout@v3
+    - uses: actions/checkout@v4
     - name: check & print release notes
       run: ./release-notes/generator.pl
     - name: Install dependencies