ci: test against PHP 8.6

Author: donatj

.github/workflows/ci.yml

@@ -11,7 +11,7 @@ jobs:
     strategy:
       matrix:
         operating-system: [ubuntu-latest]
-        php-versions: ['7.2', '7.3', '7.4', '8.0', '8.1', '8.2', '8.3', '8.4', '8.5']
+        php-versions: ['7.2', '7.3', '7.4', '8.0', '8.1', '8.2', '8.3', '8.4', '8.5', '8.6']
 
     runs-on: ${{ matrix.operating-system }}