Re-enable PHP 8.1 build on GH Actions

Author: alcaeus

.github/workflows/tests.yml

@@ -25,8 +25,7 @@ jobs:
         php-version:
           - "7.4"
           - "8.0"
-          # Re-enable after PHPC-1849 is resolved
-          # - "8.1"
+          - "8.1"
         mongodb-version:
           - "4.4"
         topology: