Minor: Spelling mistake in sample code (#1541)

Spelling mistake in sample code in ArxivRetriever instead of
get_ful_documents it should be get_full_documents
 Many thanks

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Author: mostlykloudy

src/oss/python/integrations/retrievers/arxiv.mdx

@@ -44,7 +44,7 @@ from langchain_community.retrievers import ArxivRetriever
 
 retriever = ArxivRetriever(
     load_max_docs=2,
-    get_ful_documents=True,
+    get_full_documents=True,
 )
 ```