Update test to simplify default branch migration

Contributes to https://gitlab.com/gitlab-org/gitlab/-/issues/331906

spec/features/projects/user_views_empty_project_spec.rb

@@ -7,10 +7,12 @@ RSpec.describe 'User views an empty project' do
   let_it_be(:user) { create(:user) }
 
   shared_examples 'allowing push to default branch' do
-    it 'shows push-to-master instructions' do
+    let(:default_branch) { project.default_branch_or_main }
+
+    it 'shows push-to-default-branch instructions' do
       visit project_path(project)
 
-      expect(page).to have_content('git push -u origin master')
+      expect(page).to have_content("git push -u origin #{default_branch}")
     end
   end
 
@@ -47,7 +49,7 @@ RSpec.describe 'User views an empty project' do
       it 'does not show push-to-master instructions' do
         visit project_path(project)
 
-        expect(page).not_to have_content('git push -u origin master')
+        expect(page).not_to have_content('git push -u origin')
       end
     end
   end
@@ -61,7 +63,7 @@ RSpec.describe 'User views an empty project' do
     it 'does not show push-to-master instructions nor invite members link', :aggregate_failures, :js do
       visit project_path(project)
 
-      expect(page).not_to have_content('git push -u origin master')
+      expect(page).not_to have_content('git push -u origin')
       expect(page).not_to have_button(text: 'Invite members')
     end
   end

spec/requests/api/wikis_spec.rb

@@ -611,11 +611,12 @@ RSpec.describe API::Wikis do
     let(:payload) { { file: fixture_file_upload('spec/fixtures/dk.png') } }
     let(:url) { "/projects/#{project.id}/wikis/attachments" }
     let(:file_path) { "#{Wikis::CreateAttachmentService::ATTACHMENT_PATH}/fixed_hex/dk.png" }
+    let(:branch) { wiki.default_branch }
     let(:result_hash) do
       {
         file_name: 'dk.png',
         file_path: file_path,
-        branch: 'master',
+        branch: branch,
         link: {
           url: file_path,
           markdown: "![dk](#{file_path})"