Fix bad conditional transition event check for 'gifted' segment calls

[fridaland]

Description

#437 introduced a bad conditional check in the UserStateTransitionSegmentService.
As a result, no segment calls were made.

Test process

• Modify tests accordingly, looking for gifted event
• Stub Segment calls in appropriate tests

Requirements to merge

• Replace gift_sticker with gifted
• My code follows the style guidelines of this project
• I have performed a self-review of my own code
• I have commented my code in hard-to-understand areas
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes