Bump langchain-core in /ai/gen-ai-agents/custom-rag-agent

Bumps [langchain-core](https://github.com/langchain-ai/langchain) from 0.3.66 to 0.3.80.
- [Release notes](https://github.com/langchain-ai/langchain/releases)
- [Commits](langchain-ai/langchain@langchain-core==0.3.66...langchain-core==0.3.80)

---
updated-dependencies:
- dependency-name: langchain-core
  dependency-version: 0.3.80
  dependency-type: direct:production
...

Signed-off-by: dependabot[bot] <[email protected]>

Author: dependabot[bot]

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

@@ -88,7 +88,7 @@ kiwisolver==1.4.8
 lab==8.4
 langchain==0.3.26
 langchain-community==0.3.27
-langchain-core==0.3.66
+langchain-core==0.3.80
 langchain-mcp-adapters==0.1.9
 langchain-text-splitters==0.3.8
 langchain-unstructured==0.1.6