[repo] docs: Update POWERED-BY-AI.md syntax correction (#2066)

## Linked issues

closes: https://github.com/owner/repo/issues/2061

## Details

Python feedback loop syntax correction from @app.feedback_loop to
@app.feedback_loop()

#### Change details

> Describe your changes, with screenshots and code snippets as
appropriate


## Attestation Checklist

- [ ] My code follows the style guidelines of this project

- I have checked for/fixed spelling, linting, and other errors
- I have commented my code for clarity
- I have made corresponding changes to the documentation (updating the
doc strings in the code is sufficient)
- My changes generate no new warnings
- I have added tests that validates my changes, and provides sufficient
test coverage. I have tested with:
  - Local testing
  - E2E testing in Teams
- New and existing unit tests pass locally with my changes

### Additional information

> Feel free to add other relevant information below

getting-started/CONCEPTS/POWERED-BY-AI.md

@@ -144,7 +144,7 @@ app.OnFeedbackLoop(async (turnContext, turnState, feedbackLoopData, cancellation
 ### Python
 
 ```python
-@app.feedback_loop
+@app.feedback_loop()
 async def feedback_loop(
     context: TurnContext, state: TurnState, feedback_data: FeedbackLoopData
 ):