Fix bug where SDK returned annonymous function instead of return value specified in user code to the Functions Framework.

[taeold]

Given a FireAlerts-triggered function:

export const x = onInAppFeedbackPublished((event) => true);

Users will see following error logs:

x: Error serializing return value: TypeError [ERR_INVALID_ARG_TYPE]: The first argument must be of type string or an instance of Buffer, ArrayBuffer, or Array or an Array-like Object. Received type function ([Function (anonymous)])

While the error log isn't indicative of real errors (user code still runs and background function's return value are thrown away anyway), it's still annoying.

The root issue turned out to be that the wrapTraceContext that is suppose to wrap user-defined handler was called incorrectly in couple of places.