github: bump checkout to v4

Signed-off-by: Álvaro Fernández Rojas <[email protected]>

Author: Noltari

.github/workflows/ci.yml

@@ -7,7 +7,7 @@ jobs:
     runs-on: ubuntu-20.04
     steps:
       - name: 'Check out code'
-        uses: actions/checkout@v3
+        uses: actions/checkout@v4
 
       - name: 'Install dependencies'
         run: |