Update retrievers.ipynb (#24289)

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docs/docs/tutorials/retrievers.ipynb

@@ -269,7 +269,7 @@
    "id": "b4991642-7275-40a9-b11a-e3beccbf2614",
    "metadata": {},
    "source": [
-    "Return documents based on similarity to a embedded query:"
+    "Return documents based on similarity to an embedded query:"
    ]
   },
   {