Add 8.1 to action

Author: shabbyrobe

.github/workflows/php.yml

@@ -10,7 +10,7 @@ jobs:
     runs-on: ubuntu-latest
     strategy:
       matrix:
-        php-version: ["7.2", "7.3", "7.4", "8.0"]    
+        php-version: ["7.2", "7.3", "7.4", "8.0", "8.1"]    
 
     steps:
     - name: Setup PHP ${{ matrix.php-version }}