fix: clicking three dots on post opens all dropdowns in .Post-actions

[davwheat]

Changes proposed in this pull request:

• When clicking three dots under a Post, only add the .open class to .Post-controls, not the entire .Post-actions container

Reviewers should focus on:

N/A

Screenshot (before)

bgHalgYy.1.mp4

Necessity

• Has the problem that is being solved here been clearly explained?
• If applicable, have various options for solving this problem been considered?
• For core PRs, does this need to be in core, or could it be in an extension?
• Are we willing to maintain this for years / potentially forever?

Confirmed

• Frontend changes: tested on a local Flarum installation.
• Backend changes: tests are green (run composer test).
• Core developer confirmed locally this works as intended.
• Tests have been added, or are not appropriate here.

Required changes:

• Related documentation PR: (Remove if irrelevant)
• Related core extension PRs: (Remove if irrelevant)