ci: bump checkout action to v4

Due to the transition from Node 16 to Node 20, the checkout action
needs to be updated to v4.

More info: https://github.blog/changelog/2023-09-22-github-actions-transitioning-from-node-16-to-node-20/

Signed-off-by: Geyslan Gregório <geyslan@gmail.com>

.github/workflows/test.yml

@@ -31,7 +31,7 @@ jobs:
             runs_on: s390x
             arch: 's390x'
     steps:
-      - uses: actions/checkout@v3
+      - uses: actions/checkout@v4
         name: Checkout
       - uses: ./.github/actions/setup
         name: Setup