Pin DSPy to version 2.6.27 for compatibility

DSPy versions 2.7.0+ introduce breaking changes that cause compatibility
issues with the Nova Prompt Optimizer SDK. Specifically:

- Changes to internal DSPy APIs that the SDK relies on
- Modified behavior in MIPROv2 optimizer integration
- Potential issues with structured output parsing

Pinning to 2.6.27 ensures:
- Stable SDK behavior across environments
- Consistent optimization results
- Prevents unexpected breaking changes during SDK usage
- Maintains compatibility with existing Nova SDK features

This version has been tested and verified to work correctly with
all Nova Prompt Optimizer functionality.

Author: tsanti

requirements.txt

@@ -2,7 +2,7 @@ jinja2
 boto3
 botocore
 boto3-stubs
-dspy
+dspy==2.6.27
 numpy==2.3.2
 virtualenv==20.31.2
 urllib3==2.5.0