Lint factories before spec suite

This also removes the rake task and implements Factory linting as
before(:suite) which is not recommended by the FactoryBot guys, but
we decided to implement it that way as it does not need to be
configured within CI explicitly.

lib/tasks/factory_bot.rake

@@ -1,8 +0,0 @@
-# frozen_string_literal: true
-
-namespace :factorybot do
-  desc 'Lint FactoryBot factories'
-  task lint: :environment do
-    FactoryBot.lint
-  end
-end

spec/spec_helper.rb

@@ -23,6 +23,7 @@ RSpec.configure do |config|
   # assertion/expectation library such as wrong or the stdlib/minitest
   # assertions if you prefer.
 
+  config.before(:suite) { FactoryBot.lint }
   # only runs tests with " , focus: true   "
   # config.filter_run focus: true