Add PHP 8.4 nightly to tests

So we can find problems with time.

.github/workflows/test.yml

@@ -18,7 +18,7 @@ jobs:
       fail-fast: false
       matrix:
         os: [ubuntu-latest, macos-latest, windows-latest]
-        php: ["8.1", "8.2", "8.3"]
+        php: ["8.1", "8.2", "8.3", "8.4"]
         stability: [prefer-lowest, prefer-stable]
 
     name: PHP ${{ matrix.php }} - ${{ matrix.stability }} - ${{ matrix.os }}