Composer: Update Fair namespace

[Ipstenu]

From https://github.com/fairpm/server/blob/main/composer.json#L45C5-L45C34

"fair/fair-plugin": "dev-main", -- Should this be fairpm?

[rmccue]

Looks like it should be fairpm/ which is the namespace we have on Packagist already (https://packagist.org/packages/fairpm/fair-parent-theme) and which matches GitHub (not essential but may as well) - fair/ is also already taken: https://packagist.org/packages/fair/queue