Fix creation of dynamic property in core/flarum DispatchEventsTrait

[thunder-al]

Fixes #84 #85

Changes proposed in this pull request:

Just renamed $user field of this event to $actor, because core/flarum DispatchEventsTrait trying to write ->actor field, which is not exists and php8.1+ fails because of deprecation error

• Event/WillReactToPost.php

Reviewers should focus on:

seems to WillReactToPost::$actor is not reading or writing outside of the class.
maybe we should prefer getter methods instead of direct field access?

Screenshot

dont have any

Confirmed

• Frontend changes: tested on a local Flarum installation.

• Backend changes: tests are green (run composer test).

• Tested it right on production by applying this path directly to vendor dir and liked a random post :3

Required changes:

• Related Flarum core extension PR's: (Omit this section if irrelevant)

[imorland]

Thank you for this, and sorry for the extreme delay in looking at your PR!