Ensure we generate unique usernames otherwise validations fail

Signed-off-by: Rémy Coutable <remy@rymai.me>

db/fixtures/development/18_abuse_reports.rb

@@ -4,10 +4,10 @@ module Db
       class AbuseReport
         def self.seed
           Gitlab::Seeder.quiet do
-            (::AbuseReport.default_per_page + 3).times do
+            (::AbuseReport.default_per_page + 3).times do |i|
               reported_user =
                 ::User.create!(
-                  username: "#{FFaker::Internet.user_name}-reported",
+                  username: "reported_user_#{i}",
                   name: FFaker::Name.name,
                   email: FFaker::Internet.email,
                   confirmed_at: DateTime.now,

spec/requests/api/v3/members_spec.rb

@@ -3,7 +3,7 @@ require 'spec_helper'
 describe API::V3::Members, api: true  do
   include ApiHelpers
 
-  let(:master) { create(:user) }
+  let(:master) { create(:user, username: 'master_user') }
   let(:developer) { create(:user) }
   let(:access_requester) { create(:user) }
   let(:stranger) { create(:user) }