fix: id of workflows

  The workflow is not valid. .github/workflows/ci.yml (Line: 54, Col: 3): The identifier 'prove5.8.9' is invalid. IDs may only contain alphanumeric characters, '_', and '-'. IDs must start with a letter or '_' and and must be less than 100 characters.

.github/workflows/ci.yml

@@ -51,7 +51,7 @@ jobs:
       - run: cpanm --quite --notest App::Prove
       - run: prove -lrv t
 
-  prove5.8.9:
+  prove5_8_9:
     runs-on: ubuntu-latest
     container:
       image: perl:5.8.9