build against PHP 8.1

Author: mhujer

.github/workflows/main.yml

@@ -8,7 +8,7 @@ jobs:
             fail-fast: false
             matrix:
                 operating-system: [ ubuntu-latest ]
-                php-versions: [ '8.0' ]
+                php-versions: [ '8.0', '8.1' ]
                 composer-dependencies: [ '', '--prefer-lowest' ]
                 composer-version: [ 'v1' ]
                 symfony-version: [ '' ]
@@ -25,6 +25,11 @@ jobs:
                         operating-system: windows-latest
                         coverage: xdebug
 
+                    # Windows
+                    -   php-versions: '8.1'
+                        operating-system: windows-latest
+                        coverage: xdebug
+
         steps:
             # see https://github.com/actions/checkout/issues/226#issue-606867805
             -   name: Prepare git