fix: update mailer mock to use deliver_now for Devise 5 compatibility

Devise 5 changed send_devise_notification to call deliver_now instead
of deliver. The test double only stubbed deliver, causing a failure.
This is a test-only change — real ActionMailer objects respond to both
methods.

Author: BenAkroyd

spec/models/user_spec.rb

@@ -12,7 +12,7 @@
     let(:user) { create(:user) }
 
     it "generates the reset password token" do
-      expect(Spree::UserMailer).to receive(:reset_password_instructions).with(user, anything, {}).and_return(double(deliver: true))
+      expect(Spree::UserMailer).to receive(:reset_password_instructions).with(user, anything, {}).and_return(double(deliver_now: true))
       expect { user.send_reset_password_instructions }.to change(user, :reset_password_token).to be_present
     end