Stub CSS request in invoice specs

spec/features/admin/invoice_print_spec.rb

@@ -23,6 +23,10 @@ describe '
                                                 payment_state: 'balance_due')
   end
 
+  before do
+    stub_request(:get, ->(uri) { uri.to_s.include? "/css/mail" })
+  end
+
   describe "that contains right Payment Description at Checkout information" do
     let!(:payment_method1) do
       create(:stripe_sca_payment_method, distributors: [distributor], description: "description1")

spec/views/spree/admin/orders/invoice.html.haml_spec.rb

@@ -25,6 +25,8 @@ describe "spree/admin/orders/invoice.html.haml" do
                                     display_checkout_tax_total: '10',
                                     display_checkout_total_less_tax: '8',
                                     outstanding_balance_label: 'Outstanding Balance'
+
+    stub_request(:get, ->(uri) { uri.to_s.include? "/css/mail" })
   end
 
   it "displays the customer code" do