Address Node.js 16 actions are deprecated.

Message on the run page continued with

Node.js 16 actions are deprecated.
Please update the following actions to use Node.js 20: actions/checkout@v3.
For more information see: https://github.blog/changelog/2023-09-22-github-actions-transitioning-from-node-16-to-node-20/.

.github/workflows/build-test.yaml

@@ -11,7 +11,7 @@ jobs:
   test-docker-compose:
     runs-on: ubuntu-22.04
     steps:
-      - uses: actions/checkout@v3
+      - uses: actions/checkout@v4
       - run: |
           set -e
           echo -e "dockremap:$( id -u ):1\ndockremap:200001:65535" | sudo tee -a /etc/subuid