Bump langgraph-checkpoint in /ai/gen-ai-agents/travel-agent

Bumps [langgraph-checkpoint](https://github.com/langchain-ai/langgraph) from 2.0.26 to 3.0.0.
- [Release notes](https://github.com/langchain-ai/langgraph/releases)
- [Commits](langchain-ai/langgraph@checkpoint==2.0.26...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/travel-agent/requirements.txt

@@ -77,7 +77,7 @@ langchain-community==0.3.24
 langchain-core==0.3.60
 langchain-text-splitters==0.3.8
 langgraph==0.4.5
-langgraph-checkpoint==2.0.26
+langgraph-checkpoint==3.0.0
 langgraph-prebuilt==0.1.8
 langgraph-sdk==0.1.69
 langsmith==0.3.42