PHPStan: Make get_subscribed_events rule to check return type supports variables

[CrochetFeve0251]

Is your feature request related to a problem? Please describe.
Original
The original issue was expected to handle all cases but we discovered while implementing that we need two different logics for varaibles and array.

Describe the solution you'd like
This issue should handle the return from the method get_subscribed_events and make sure it is the right format when a variable is returned.
Describe alternatives you've considered
A clear and concise description of any alternative solutions or features you've considered.

Additional context
Add any other context or screenshots about the feature request here.