[CI] Streamline GitHub workflow configuration for tests (#368)

- The strategy option is removed. This is superfluous as no build matrix is defined.
- The actions/checkout action is updated to version 4.

Releases: main, 12.4

.github/workflows/tests.yml

@@ -8,15 +8,11 @@ jobs:
   testsuite:
     name: all tests
     runs-on: ubuntu-latest
-    strategy:
-      # This prevents cancellation of matrix job runs, if one or more already failed
-      # and let the remaining matrix jobs be executed anyway.
-      fail-fast: false
     env:
       php: '8.1'
     steps:
       - name: Checkout
-        uses: actions/checkout@v3
+        uses: actions/checkout@v4
 
       - name: Install testing system
         run: Build/Scripts/runTests.sh -p ${{ env.php }} -s composerUpdate