Fixed Import Error type in base.py (langchain-ai#10209)

I have revamped the code to ensure uniform error handling for
ImportError. Instead of the previous reliance on ValueError, I have
adopted the conventional practice of raising ImportError and providing
informative error messages. This change enhances code clarity and
clearly signifies that any problems are associated with module imports.

libs/langchain/langchain/vectorstores/redis/base.py

@@ -1220,7 +1220,7 @@ def _create_index(self, dim: int = 1536) -> None:
             )
 
         except ImportError:
-            raise ValueError(
+            raise ImportError(
                 "Could not import redis python package. "
                 "Please install it with `pip install redis`."
             )