run CI using PHP 8.3

Just for consistency with the version we bootstrap, since a few of the platform installer/generator related tests run directly in RSpec with the 'local' PHP, not via Hatchet

Author: dzuelke

.github/workflows/ci.yml

@@ -48,7 +48,7 @@ jobs:
       - name: Install PHP and Composer
         uses: shivammathur/setup-php@v2
         with:
-          php-version: "8.2"
+          php-version: "8.3"
           tools: "composer:2.8"
       - name: Install packages from requirements.txt, plus s5cmd (for some tests)
         run: |