[Bug] Issue when failing to build activity failure

[cretz]

Describe the bug

When activity fails, but the failure can't be converted for whatever reason, we build a general failure at

sdk-python/temporalio/worker/_activity.py

Lines 507 to 510 in 723d234

	completion.result.Clear()
	completion.result.failed.failure.message = (
	f"Failed building exception result: {inner_err}"
	)

. But we aren't properly building this by putting application failure info in it. We fixed the same issue in .NET recently: temporalio/sdk-dotnet#353. We need to do the same here.