fix(mentions): correctly convert a 3 char. hex color to a 6 char. one

[Ornanovitch]

Fixes #3693

Changes proposed in this pull request:

Quick fix for

framework/extensions/mentions/src/ConfigureMentions.php

Lines 206 to 209 in 67dd2c2

	$hexNumbers = Str::replace('#', '', $hexColor);
	if (Str::length($hexNumbers) === 3) {
	$hexNumbers += $hexNumbers;
	}

, which seems to be unsupported (string + string operation)

Reviewers should focus on:

The before/after behavior should be tested first. See the steps to reproduce in #3693

Screenshot

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]

I have a branch waiting for #3653 to be merged first, in which I drop te PHP code for YIQ computation, to reduce the overhead of repeating the logic for it both back and front ends.

So let's not move forward with this for now.

[Ornanovitch]

Great!

[askvortsov1]

Could we do this as a string format instead?

[Ornanovitch]

superseded by #3723