[Messenger] Fix a typo on Messenger handler results example

[alepdev]

This fixes typo on the Messenger handler results sample snippet by renaming Result object since the definition in the import and the name used in the return type of the function did not match.

I fixed with ListItemsResult instead of ListItemsQueryResult but tell me which one is better.

[javiereguiluz]

Alessio, thanks for fixing this bug. We did a couple of changes while merging:

• We merged in 4.4 (and 5.1 and 5.x) because 4.2 is no longer maintained. We only merge on maintained branches. You can find those branches here: https://symfony.com/releases
• As you mentioned, the fix can be reversed to use the imported ListItemsQueryResult class. We did that because the class name looked more consistent with the existing ListItemsQuery.

Thanks!