Commit message generation customization has regressed

- Copilot Chat Extension Version:
- VS Code Version: 1.133.0
- OS Version: Mac
- Feature (e.g. agent/edit/ask mode):
- Selected model (e.g. GPT 4.1, Claude 3.7 Sonnet):
- Logs:

Steps to Reproduce:

1. Define GitHub Copilot chat commit message generation instructions
2. Try having copilot auto generate the commit message

Expected:

Commit message autogenerated.

Actual:

Generate commit message spinner briefly spins but not message is generated. If you remove the custom instructions, it starts working again.

This had regressed in at least 1.132 or maybe even 1.131.