Use Composer 2.8 in CI for now

Author: axlon

.github/workflows/tests.yml

@@ -110,7 +110,7 @@ jobs:
         uses: shivammathur/setup-php@v2
         with:
           php-version: ${{ matrix.php }}
-          tools: composer:v2
+          tools: composer:2.8
 
       - name: Install dependencies
         run: |