Fix documents for RetrievalQAWithSourcesChain (#11292)

- **Description:** Fix typo about `RetrievalQAWithSourceChain` ->
`RetrievalQAWithSourcesChain`
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docs/snippets/modules/chains/popular/vector_db_qa_with_sources.mdx

@@ -41,7 +41,7 @@ result["source_documents"]
 
 </CodeOutputBlock>
 
-Alternatively, if our document have a "source" metadata key, we can use the `RetrievalQAWithSourceChain` to cite our sources:
+Alternatively, if our document have a "source" metadata key, we can use the `RetrievalQAWithSourcesChain` to cite our sources:
 
 ```python
 docsearch = Chroma.from_texts(texts, embeddings, metadatas=[{"source": f"{i}-pl"} for i in range(len(texts))])