Fix type error

Author: zastrowm

src/strands/tools/registry.py

@@ -54,7 +54,7 @@ def process_tools(self, tools: List[Any]) -> List[str]:
         """
         tool_names = []
 
-        def add_tool(tool: Any):
+        def add_tool(tool: Any) -> None:
             # Case 1: String file path
             if isinstance(tool, str):
                 # Extract tool name from path