docs: update `hub.pull("rlm/map-prompt")` to `hub.pull("rlm/reduce-prompt")` for reduce prompt (#22088)

**PR message**: 
Update `hub.pull("rlm/map-prompt")` to `hub.pull("rlm/reduce-prompt")`
in summarization.ipynb

**Description:** 
Fix typo in prompt hub link from `reduce_prompt =
hub.pull("rlm/map-prompt")` to `reduce_prompt =
hub.pull("rlm/reduce-prompt")` following next issue

**Issue:** #22014

Co-authored-by: Bagatur <22008038+baskaryan@users.noreply.github.com>

docs/docs/tutorials/summarization.ipynb

@@ -374,7 +374,7 @@
    "outputs": [],
    "source": [
     "# Note we can also get this from the prompt hub, as noted above\n",
-    "reduce_prompt = hub.pull(\"rlm/map-prompt\")"
+    "reduce_prompt = hub.pull(\"rlm/reduce-prompt\")"
    ]
   },
   {