ci: upgrade php version to launch roave/backward-compatibility-check

.github/workflows/bc.yml

@@ -8,6 +8,10 @@ jobs:
       - uses: actions/checkout@v3
         with:
           fetch-depth: 0
+      - name: Set up PHP
+        uses: shivammathur/setup-php@v2
+        with:
+          php-version: 8.3
       - name: Composer install
         run: composer require --dev roave/backward-compatibility-check
       - name: Roave BC Check