Python: Sets a valid default content filter code to ResponsibleAIPolicyViolation (#4715)

### Motivation and Context

When the RAI response doesn't contain a `code` the class
`ContentFilterAIException` would fail to initialize because it was
setting `""` as content_filter_code. This sets
`"ResponsibleAIPolicyViolation"` instead in that case.

Fixes #4709 

### Contribution Checklist

<!-- Before submitting this PR, please make sure: -->

- [X] The code builds clean without any errors or warnings
- [X] The PR follows the [SK Contribution
Guidelines](https://github.com/microsoft/semantic-kernel/blob/main/CONTRIBUTING.md)
and the [pre-submission formatting
script](https://github.com/microsoft/semantic-kernel/blob/main/CONTRIBUTING.md#development-scripts)
raises no violations
- [X] All unit tests pass, and I have added new tests where possible
- [X] I didn't break anyone 😄

Co-authored-by: Evan Mattson <[email protected]>

python/semantic_kernel/connectors/ai/open_ai/exceptions/content_filter_ai_exception.py

@@ -75,7 +75,9 @@ class ContentFilterAIException(AIException):
         self._param = inner_exception.param
 
         inner_error = inner_exception.body.get("innererror", {})
-        self._content_filter_code = ContentFilterCodes(inner_error.get("code", ""))
+        self._content_filter_code = ContentFilterCodes(
+            inner_error.get("code", ContentFilterCodes.RESPONSIBLE_AI_POLICY_VIOLATION.value)
+        )
         self._content_filter_result = dict(
             [
                 key,