Add workflows permission to schema

Add 'workflows' as a valid permission scope in the permissions-mapping
schema. The workflows permission supports only 'write' (or none),
matching the GitHub App permissions model where workflows: write
allows updating GitHub Actions workflow files.

This enables autocomplete and validation for 'permissions: workflows:'
in workflow YAML files.

workflow-parser/src/workflow-v1.0.json

@@ -1649,6 +1649,10 @@
           "statuses": {
             "type": "permission-level-any",
             "description": "Commit statuses."
+          },
+          "workflows": {
+            "type": "permission-level-write-or-no-access",
+            "description": "Update GitHub Actions workflow files."
           }
         }
       }