Test against php 8.1

Author: Sergiy Petrov

.github/workflows/build.yaml

@@ -10,7 +10,7 @@ jobs:
         runs-on: ubuntu-latest
         strategy:
             matrix:
-                php: [ '7.4', '8.0' ]
+                php: [ '7.4', '8.0', '8.1' ]
                 composer-flags: [ '' ]
                 phpunit-flags: [ '--coverage-text' ]
         steps: