Python: Make sure to log errors from async handlers (#2820)

## Motivation and Context
We were skipping logging of the errors occurred during execution of
asynchronous Python handlers due to the question mark at the end:
```
result.await.map(|r| #{pyo3}::Python::with_gil(|py| r.extract::<$output>(py)))? // <-
```

Any exception thrown in asynchronous Python handlers will be logged
properly with this change.

## Checklist
<!--- If a checkbox below is not applicable, then please DELETE it
rather than leaving it unchecked -->
- [ ] I have updated `CHANGELOG.next.toml` if I made changes to the
smithy-rs codegen or runtime crates
- [ ] I have updated `CHANGELOG.next.toml` if I made changes to the AWS
SDK, generated SDK code, or SDK runtime crates

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