CI: Add PHP 8.3

Author: alecpl

.github/workflows/tests.yml

@@ -12,7 +12,7 @@ jobs:
     strategy:
       fail-fast: true
       matrix:
-        php: ["5.6", "7.0", "7.1", "7.2", "7.3", "7.4", "8.0", "8.1", "8.2"]
+        php: ["5.6", "7.0", "7.1", "7.2", "7.3", "7.4", "8.0", "8.1", "8.2", "8.3"]
 
     name: PHP ${{ matrix.php }}/Linux