CI: test on PHP-8 stable

Author: marc-mabe

.github/workflows/test.yml

@@ -23,7 +23,7 @@ jobs:
             CODE_COVERAGE: true
           - PHP_VERSION: 7.4
             CODE_COVERAGE: true
-          - PHP_VERSION: 8.0-rc
+          - PHP_VERSION: 8.0
             CODE_COVERAGE: true
 
     steps: