Add PHP 8.1 to the build matrix.

Author: jmalloc

.github/workflows/ci.yml

@@ -13,7 +13,7 @@ jobs:
     strategy:
       fail-fast: false
       matrix:
-        php: ['7.3', '7.4', '8.0']
+        php: ['7.3', '7.4', '8.0', '8.1']
     steps:
     - name: Set up PHP
       uses: shivammathur/setup-php@master