Speed up group finder specs by using let_it_be in shared context

spec/support/shared_contexts/finders/group_projects_finder_shared_contexts.rb

 # frozen_string_literal: true
 
 RSpec.shared_context 'GroupProjectsFinder context' do
-  let(:group) { create(:group) }
-  let(:subgroup) { create(:group, parent: group) }
-  let(:current_user) { create(:user) }
+  let_it_be(:group) { create(:group) }
+  let_it_be(:subgroup) { create(:group, parent: group) }
+  let_it_be(:current_user) { create(:user) }
   let(:params) { {} }
   let(:options) { {} }
 
   let(:finder) { described_class.new(group: group, current_user: current_user, params: params, options: options) }
 
-  let!(:public_project) { create(:project, :public, group: group, path: '1') }
-  let!(:private_project) { create(:project, :private, group: group, path: '2') }
-  let!(:shared_project_1) { create(:project, :public, path: '3') }
-  let!(:shared_project_2) { create(:project, :private, path: '4') }
-  let!(:shared_project_3) { create(:project, :internal, path: '5') }
-  let!(:subgroup_project) { create(:project, :public, path: '6', group: subgroup) }
-  let!(:subgroup_private_project) { create(:project, :private, path: '7', group: subgroup) }
+  let_it_be(:public_project) { create(:project, :public, group: group, path: '1') }
+  let_it_be(:private_project) { create(:project, :private, group: group, path: '2') }
+  let_it_be(:shared_project_1) { create(:project, :public, path: '3') }
+  let_it_be(:shared_project_2) { create(:project, :private, path: '4') }
+  let_it_be(:shared_project_3) { create(:project, :internal, path: '5') }
+  let_it_be(:subgroup_project) { create(:project, :public, path: '6', group: subgroup) }
+  let_it_be(:subgroup_private_project) { create(:project, :private, path: '7', group: subgroup) }
 
   before do
     shared_project_1.project_group_links.create!(group_access: Gitlab::Access::MAINTAINER, group: group)