test(github): Run tests on any push or pull request

.github/workflows/testing.yml

 name: Tests
-on:
-  push:
-    branches: [ 8.3.x, 8.x-3.x ]
-  pull_request:
-    branches: [ 8.3.x, 8.x-3.x ]
+on: [push, pull_request]
 jobs:
   testing:
     name: PHP ${{ matrix.php-versions }}