Adjust size of FontAwesome icons on extensions list to match size of custom images

[rob006]

Before:

After:

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.

[SychO9]

@rob006 are you using any custom themes? this does not seem to be the case in default flarum, font sizes are already made relative to the size

[rob006]

@SychO9 You're right, this is caused by malago/flarum-achievements: