[Chore] Use flex from shivammathur/setup-php

Author: loic425

.github/workflows/build.yml

@@ -41,13 +41,12 @@ jobs:
                 with:
                     php-version: "${{ matrix.php }}"
                     coverage: none
+                    tools: 'composer:v2, flex'
 
             -
                 name: Restrict Symfony version
                 if: matrix.symfony != ''
                 run: |
-                    composer global config --no-plugins allow-plugins.symfony/flex true
-                    composer global require --no-progress --no-scripts --no-plugins "symfony/flex:^1.10"
                     composer config extra.symfony.require "${{ matrix.symfony }}"
                     (cd src/Component && composer config extra.symfony.require "${{ matrix.symfony }}")