fix doc example issue

Author: Wh1isper

docs/models/anthropic.md

@@ -208,6 +208,8 @@ async def main():
 When cache points from all sources (settings + `CachePoint` markers) exceed 4, Pydantic AI automatically removes excess cache points from **older message content** (keeping the most recent ones):
 
 ```python {test="skip"}
+from pydantic_ai import Agent, CachePoint
+from pydantic_ai.models.anthropic import AnthropicModelSettings
 agent = Agent(
     'anthropic:claude-sonnet-4-5',
     system_prompt='Instructions...',