When in the trial flow, hide intention question

While in the registration flow, don't ask a user what they want to do
(which allows the user to bypass the registration). Instead, continue
their trial flow.

part of:
https://gitlab.com/gitlab-org/gitlab/-/issues/351142

ee/app/views/registrations/welcome/_joining_project.html.haml

 - return unless Gitlab.dev_env_or_com?
+- return if in_trial_flow?
 
 - experiment(:bypass_registration, user: current_user) do |e|
   - e.publish_to_database

ee/spec/views/registrations/welcome/show.html.haml_spec.rb

@@ -28,15 +28,15 @@ RSpec.describe 'registrations/welcome/show' do
 
     subject { rendered }
 
-    where(:redirect_path, :signup_onboarding_enabled, :show_progress_bar, :flow, :is_continue) do
-      '/-/subscriptions/new'    | false | true  | :subscription | true
-      '/-/subscriptions/new'    | true  | true  | :subscription | true
-      '/-/trials/new'           | false | false | :trial        | true
-      '/-/trials/new'           | true  | false | :trial        | true
-      '/oauth/authorize/abc123' | false | false | nil           | false
-      '/oauth/authorize/abc123' | true  | false | nil           | false
-      nil                       | false | false | nil           | false
-      nil                       | true  | true  | nil           | true
+    where(:redirect_path, :signup_onboarding_enabled, :show_progress_bar, :flow, :is_continue, :show_joining_question) do
+      '/-/subscriptions/new'    | false | true  | :subscription | true  | true
+      '/-/subscriptions/new'    | true  | true  | :subscription | true  | true
+      '/-/trials/new'           | false | false | :trial        | true  | false
+      '/-/trials/new'           | true  | false | :trial        | true  | false
+      '/oauth/authorize/abc123' | false | false | nil           | false | true
+      '/oauth/authorize/abc123' | true  | false | nil           | false | true
+      nil                       | false | false | nil           | false | true
+      nil                       | true  | true  | nil           | true  | true
     end
 
     with_them do
@@ -60,7 +60,7 @@ RSpec.describe 'registrations/welcome/show' do
         context 'when in the candidate variant' do
           let(:experiments) { { bypass_registration: :candidate } }
 
-          it { is_expected.to have_selector('#joining_project_true') }
+          it { is_expected_to_show_joining_question(show_joining_question) }
         end
       end
 
@@ -90,6 +90,14 @@ RSpec.describe 'registrations/welcome/show' do
     end
   end
 
+  def is_expected_to_show_joining_question(status)
+    if status
+      is_expected.to have_selector('#joining_project_true')
+    else
+      is_expected.not_to have_selector('#joining_project_true')
+    end
+  end
+
   context 'rendering the hidden email opt in checkbox' do
     subject { render }