Move let into private method in Updating a project spec

This value doesn't change in any of the contexts, so using a `let` block
is of limited value. Also it will avoid triggering a violation of
`RSpec/MultipleMemoizedHelpers` in a later commit.

Author: floehopper

spec/features/project/updating_a_project_spec.rb

@@ -3,7 +3,6 @@
 require 'rails_helper'
 
 RSpec.describe 'Updating a project', type: :request do
-  let(:headers) { { Authorization: UserProfileMock::TOKEN } }
   let(:project_type) { Project::Types::PYTHON }
   let(:user_id) { owner.id }
   let!(:project) { create(:project, name: 'Test Project', user_id:, locale: 'en', project_type:) }
@@ -78,4 +77,10 @@
       expect(data[:name]).to eq('Test Project')
     end
   end
+
+  private
+
+  def headers
+    { Authorization: UserProfileMock::TOKEN }
+  end
 end