Fix closing bracket in length-based selector snippet (#11294)

**Description:**

Fix a forgotten closing bracket in the length-based selector snippet

Co-authored-by: Eugene Yurtsev <eyurtsev@gmail.com>

docs/snippets/modules/model_io/prompts/example_selectors/length_based.mdx

@@ -11,6 +11,7 @@ examples = [
     {"input": "energetic", "output": "lethargic"},
     {"input": "sunny", "output": "gloomy"},
     {"input": "windy", "output": "calm"},
+]
 
 example_prompt = PromptTemplate(
     input_variables=["input", "output"],