Run PHPStan on every PHP version in CI workflow

Author: lkrms

.github/workflows/ci.yml

@@ -100,6 +100,10 @@ jobs:
       matrix:
         php-version:
           - "8.4"
+          - "8.3"
+          - "8.2"
+          - "8.1"
+          - "8.0"
           - "7.4"
 
     runs-on: ubuntu-24.04