chore: update documentation and action

Author: m-seidel

.github/workflows/php.yml

@@ -12,7 +12,7 @@ jobs:
     strategy:
       matrix:
         operating-system: ['ubuntu-latest']
-        php-versions: ['7.4', '8.0']
+        php-versions: ['7.4']
         phpunit-versions: ['latest']
     steps:
     - name: Checkout