docs: Update Google GenAI doc formatting (langchain-ai#7318)

docs/core_docs/docs/integrations/chat/google_generativeai.ipynb

@@ -801,7 +801,7 @@
       "id": "a464c1a9",
       "metadata": {},
       "source": [
-        "### Context Caching\n",
+        "## Context Caching\n",
         "\n",
         "Context caching allows you to pass some content to the model once, cache the input tokens, and then refer to the cached tokens for subsequent requests to reduce cost. You can create a `CachedContent` object using `GoogleAICacheManager` class and then pass the `CachedContent` object to your `ChatGoogleGenerativeAIModel` with `enableCachedContent()` method."
       ]