Remove --ignore-platform-req=php for PHP 8

Author: kelunik

.github/workflows/ci.yml

@@ -26,7 +26,6 @@ jobs:
 
           - operating-system: 'ubuntu-latest'
             php-version: '8.0'
-            composer-flags: '--ignore-platform-req=php'
 
           - operating-system: 'windows-latest'
             php-version: '7.4'