Add PHP 8.4 unit tests to CI

Author: JanJakes

.github/workflows/phpunit-tests.yml

@@ -20,7 +20,7 @@ jobs:
         # NOTE: There does not appear to be a single phpunit version that supports all
         # PHP versions tested here. For now, we are removing PHP 7.0. and 7.1 tests
         # in order to run a single phpunit version for PHP 7.2 and up.
-        php: [ '7.2', '7.3', '7.4', '8.0', '8.1', '8.2', '8.3' ]
+        php: [ '7.2', '7.3', '7.4', '8.0', '8.1', '8.2', '8.3', '8.4' ]
 
     with:
       os: ${{ matrix.os }}