Test against PHP 8.1 (#30)

* Test against PHP 8.1

* Don't run lowest dependencies on PHP 8.1

Author: svenluijten

.github/workflows/run-tests.yml

@@ -9,8 +9,11 @@ jobs:
         strategy:
             matrix:
                 os: [ubuntu-latest, windows-latest]
-                php: [7.4, 8.0]
+                php: [7.4, 8.0, 8.1]
                 dependency-version: [lowest, highest]
+                exclude:
+                    - php: 8.1
+                      dependency-version: lowest
 
         name: PHP ${{ matrix.php }} - ${{ matrix.dependency-version }} on ${{ matrix.os }}