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']
+        php-versions: ['7.4', '8.0']
         phpunit-versions: ['latest']
     steps:
     - name: Checkout

README.md

@@ -17,7 +17,7 @@ composer require staffbase/plugins-sdk-php
 
 Dependencies are also managed by Composer. When using this repository keep the following dependencies in mind (cf. [composer.json](composer.json)):
 
-* php: >=7.4.0
+* php: ^7.4.0 || ^8.0
 * lcobucci/jwt: ^4.1
 
 ## API Reference