fix CI by reverting #17020

Author: HeahDude

.github/workflows/ci.yaml

@@ -116,11 +116,6 @@ jobs:
             if: ${{ steps.find-files.outputs.files }}
             run: composer create-project symfony-tools/code-block-checker:@dev _checker
 
-          - name: Allow Flex
-            if: ${{ steps.find-files.outputs.files }}
-            run: |
-              composer config --no-plugins allow-plugins.symfony/flex true
-
           - name: Install test application
             if: ${{ steps.find-files.outputs.files }}
             run: |