deps: Support PHP 8.4

Adds PHP 8.4 to the CI matrix.

See firebase#572 and firebase#578

Author: ruudk

.github/workflows/tests.yml

@@ -10,7 +10,7 @@ jobs:
     runs-on: ubuntu-latest
     strategy:
       matrix:
-        php: [ "8.0", "8.1", "8.2", "8.3" ]
+        php: [ "8.0", "8.1", "8.2", "8.3", "8.4" ]
     name: PHP ${{matrix.php }} Unit Test
     steps:
       - uses: actions/checkout@v2