Fix for code snippet in documentation (#8290)

- Description: I fixed an issue in the code snippet related to the
variable name and the evaluation of its length. The original code used
the variable "docs," but the correct variable name is "docs_svm" after
using the SVMRetriever.
- maintainer: @baskaryan
- Twitter handle: @iamreechi_

Co-authored-by: iamreechi <richieakparuorji>

docs/extras/use_cases/question_answering/index.mdx

@@ -189,7 +189,7 @@ All retrievers implement some common methods, such as `get_relevant_documents()`
 from langchain.retrievers import SVMRetriever
 svm_retriever = SVMRetriever.from_documents(all_splits,OpenAIEmbeddings())
 docs_svm=svm_retriever.get_relevant_documents(question)
-len(docs)
+len(docs_svm)
 ```