fix: correct mypy type: ignore error codes (arg-type, not return-value)

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: tirth8205

code_review_graph/analysis.py

@@ -49,7 +49,7 @@ def find_hub_nodes(store: GraphStore, top_n: int = 10) -> list[dict]:
         })
 
     scored.sort(
-        key=lambda x: x.get("total_degree", 0),  # type: ignore[return-value]
+        key=lambda x: x.get("total_degree", 0),  # type: ignore[arg-type]
         reverse=True,
     )
     return scored[:top_n]
@@ -184,7 +184,7 @@ def find_knowledge_gaps(store: GraphStore) -> dict[str, list[dict]]:
                 "degree": d,
             })
     untested_hotspots.sort(
-        key=lambda x: x.get("degree", 0),  # type: ignore[return-value]
+        key=lambda x: x.get("degree", 0),  # type: ignore[arg-type]
         reverse=True,
     )