Fix framework typo in detection post process error

[diaz3z]

Fixes a typo in post_process_detection.py where self.framwork was used instead of self.framework.

Without this fix, unsupported framework values can trigger an AttributeError instead of the intended ValueError.

Validation:

• Ran python -m py_compile runtimes/examples/python/utils/post_process/post_process_detection.py