add php 8.1 to actions matrix

Author: vyuldashev

.github/workflows/tests.yml

@@ -13,7 +13,7 @@ jobs:
     strategy:
       fail-fast: true
       matrix:
-        php: [8.0, 8.0]
+        php: [8.0, 8.1]
         stability: [prefer-lowest, prefer-stable]
 
     name: PHP ${{ matrix.php }} - ${{ matrix.stability }}