Replaced instances of raising ValueError with raising ImportError. (#9388)

Refactored code to ensure consistent handling of ImportError. Replaced
instances of raising ValueError with raising ImportError.

The choice of raising a ValueError here is somewhat unconventional and
might lead to confusion for anyone reading the code. Typically, when
dealing with import-related errors, the recommended approach is to raise
an ImportError with a descriptive message explaining the issue. This
provides a clearer indication that the problem is related to importing
the required module.

@hwchase17 , @baskaryan , @eyurtsev 

Thanks
Aashish

---------

Co-authored-by: Bagatur <baskaryan@gmail.com>

libs/langchain/langchain/embeddings/huggingface.py

@@ -149,7 +149,7 @@ class HuggingFaceInstructEmbeddings(BaseModel, Embeddings):
                 self.model_name, cache_folder=self.cache_folder, **self.model_kwargs
             )
         except ImportError as e:
-            raise ValueError("Dependencies for InstructorEmbedding not found.") from e
+            raise ImportError("Dependencies for InstructorEmbedding not found.") from e
 
     class Config:
         """Configuration for this pydantic object."""

libs/langchain/langchain/utilities/duckduckgo_search.py

@@ -30,7 +30,7 @@ class DuckDuckGoSearchAPIWrapper(BaseModel):
         try:
             from duckduckgo_search import DDGS  # noqa: F401
         except ImportError:
-            raise ValueError(
+            raise ImportError(
                 "Could not import duckduckgo-search python package. "
                 "Please install it with `pip install duckduckgo-search`."
             )