Use GRANITE_TESTING in Summarize recipe

[fayvor]

pm#149

• Use GRANITE_TESTING to speed up Summarize testing

PR Checklist

• [ ] Commits signed: All commits must be GPG or SSH signed.
• [ ] DCO Compliance: Developer Certificate of Origin (DCO) applies to the code, documentation, and any example data provided. Ensure commits are signed off.
• [ ] Notebook outputs cleared: Ensure all notebook outputs are cleared.
• [ ] Automated testing: Add the recipe to the automated tests.
• [ ] Test in Google Colab:
  • [ ] Test that it works in Google Colab (Python 3.10.12).
  • [ ] Colab has its own package set and Python version, so ensure compatibility.
• [ ] Test locally:
  • [ ] Ensure the code works in a fresh Python virtual environment (venv).
• [ ] Flexible LLM platform support:
  • [ ] The platform should be easily switchable. Use LangChain for now.
  • [ ] Include !pip install git+https://github.com/ibm-granite-community/granite-kitchen in the instructions.
• [ ] Example data: Follow the example data guidance.
• [ ] README.md updates:
  • [ ] Add a link to the recipe in the Table of Contents (ToC).
  • [ ] Include a Colab button after that link.