Docs: Fix broken line breaks in snippets (#11523)

**Description:**
This PR fix some code snippets that have raw `\n`'s instead of actual
line breaks.

**Issue:**
Currently some snippets look like this:

![image](https://github.com/langchain-ai/langchain/assets/18213435/355b4911-38e9-4ba4-8570-f928557b6c13)

Affected pages:
-
https://python.langchain.com/docs/integrations/providers/predictionguard#example-usage
-
https://python.langchain.com/docs/modules/agents/how_to/custom_llm_agent#set-up-environment
-
https://python.langchain.com/docs/modules/chains/foundational/llm_chain#get-started
-
https://python.langchain.com/docs/integrations/providers/shaleprotocol#how-to

**Tag maintainer:**
@hwchase17

docs/snippets/modules/agents/how_to/custom_llm_agent.mdx

@@ -20,7 +20,9 @@ Do necessary imports, etc.
 ```python
 from langchain.agents import Tool, AgentExecutor, LLMSingleActionAgent, AgentOutputParser
 from langchain.prompts import StringPromptTemplate
-from langchain.llms import OpenAI\nfrom langchain.utilities import SerpAPIWrapper\nfrom langchain.chains import LLMChain
+from langchain.llms import OpenAI
+from langchain.utilities import SerpAPIWrapper
+from langchain.chains import LLMChain
 from typing import List, Union
 from langchain.schema import AgentAction, AgentFinish, OutputParserException
 import re