ci: fix matrix in ci.yml

8.0 is an integer in yml, we want '8.0' (string)

Author: bytestream

.github/workflows/ci.yml

@@ -9,7 +9,7 @@ jobs:
         strategy:
             fail-fast: true
             matrix:
-                php: [7.2, 7.3, 7.4, 8.0, 8.1]
+                php: ['7.2', '7.3', '7.4', '8.0', '8.1']
                 stability: [prefer-stable]
 
         name: PHP ${{ matrix.php }} - ${{ matrix.stability }}