Make PHP 8.4 test experimental

Author: tuupola

.github/workflows/tests.yml

@@ -4,9 +4,14 @@ jobs:
   build:
     strategy:
       fail-fast: false
+      continue-on-error: ${{ matrix.experimental }}
       matrix:
         operating-system: [ubuntu-latest]
         php-versions: ["7.2", "7.3", "7.4", "8.0", "8.1", "8.2", "8.3"]
+        experimental: [false]
+        include:
+          - version: "8.4"
+            experimental: true
     runs-on: ${{ matrix.operating-system }}
     steps:
       - name: Checkout code