ci: upgrade to actions/checkout@v3

This uses the new node 16 version (see [1]), which is the future proof
version, since node 12 will be deprecated by summer 2023 (see [2]).

[1] upstream commits:
8f9e05e482
a12a3943b4

[2] https://github.blog/changelog/2022-09-22-github-actions-all-actions-will-begin-running-on-node16-instead-of-node12/

.github/workflows/trigger-gitlab.yml

@@ -22,7 +22,7 @@ jobs:
           sudo apt install -y jq
 
       - name: Clone repository
-        uses: actions/checkout@v2
+        uses: actions/checkout@v3
         with:
           ref: ${{ github.event.workflow_run.head_sha }}
           fetch-depth: 0