fix: Suppress pandas import type error (pre-existing issue)

- Add type: ignore[import-untyped] comment for pandas import
- This is a pre-existing issue unrelated to external knowledge directory feature
- Allows CI type-checker to pass while maintaining type safety for new code

Co-Authored-By: João <joao@crewai.com>

src/crewai/knowledge/source/excel_knowledge_source.py

@@ -132,7 +132,7 @@ class ExcelKnowledgeSource(BaseKnowledgeSource):
     def _import_dependencies(self):
         """Dynamically import dependencies."""
         try:
-            import pandas as pd
+            import pandas as pd  # type: ignore[import-untyped]
 
             return pd
         except ImportError as e: