Timeout of scheduled lambda is broken since v.9.3.0

If scheduled lambda doesn't return a truthy value, it will result in a timeout even if the handler function is processed normally.

For example, if you specify a scheduled lambda like:
```
timeout: 5
events:
- schedule: cron(20 * * * *)
```

And make the handler to be like this:
```
def handler(event, context):
print("hello")
return

```
And then run serverless-offline, it will result in a timeout. However, if you change `return` to `return True`, it will work as it should and timeout doesn't happen.

Now we are forced to make our scheduled lambdas to return True if we want to simulate them.

Start by reproducing the issue with serverless-offline using the scheduled configuration and the handler that prints "hello" and returns no value. Trace the scheduled lambda timeout path; done means a normally processed handler no longer times out when it returns a falsy value, while the existing truthy-return behavior remains valid.

Written by the indexing model from the issue text.