Bump langgraph-checkpoint in /ai/gen-ai-agents/custom-rag-agent

Bumps [langgraph-checkpoint](https://github.com/langchain-ai/langgraph) from 2.1.0 to 3.0.0.
- [Release notes](https://github.com/langchain-ai/langgraph/releases)
- [Commits](langchain-ai/langgraph@checkpoint==2.1.0...checkpoint==3.0.0)

---
updated-dependencies:
- dependency-name: langgraph-checkpoint
  dependency-version: 3.0.0
  dependency-type: direct:production
...

Signed-off-by: dependabot[bot] <support@github.com>

Author: dependabot[bot]

ai/gen-ai-agents/custom-rag-agent/requirements.txt

@@ -94,7 +94,7 @@ langchain-text-splitters==0.3.8
 langchain-unstructured==0.1.6
 langdetect==1.0.9
 langgraph==0.5.0
-langgraph-checkpoint==2.1.0
+langgraph-checkpoint==3.0.0
 langgraph-prebuilt==0.5.1
 langgraph-sdk==0.1.55
 langsmith==0.4.4