fix: Add type annotation to fix mypy error

Author: cfsmp3

mod_ci/controllers.py

@@ -317,10 +317,11 @@ def _diagnose_missing_artifact(repository, commit_sha: str, expected_workflow: s
     :return: A descriptive error message
     """
     from collections import defaultdict
+    from typing import DefaultDict, Optional
 
     try:
         # Build workflow name lookup
-        workflow = defaultdict(lambda: None)
+        workflow: DefaultDict[int, Optional[str]] = defaultdict(lambda: None)
         for active_workflow in repository.get_workflows():
             workflow[active_workflow.id] = active_workflow.name