enabled php 8.1

Author: eerison

.github/workflows/tests.yml

@@ -8,7 +8,7 @@ jobs:
     strategy:
       matrix:
         os: [ubuntu-latest, windows-latest]
-        php: ['7.4', '8.0']
+        php: ['7.4', '8.0', '8.1']
         dependency-version: [prefer-stable]
 
     name: PHP ${{ matrix.php }} - ${{ matrix.os }} - ${{ matrix.dependency-version }}