Update specs to expect :defer as default loading strategy

Updates configuration_spec.rb to reflect the new default behavior where
generated_component_packs_loading_strategy defaults to :defer instead of
:async (Shakapacker >= 8.2.0) or :sync (Shakapacker < 8.2.0).

This change aligns with the race condition fix that makes :defer the
universal default to ensure component registrations complete before
React hydration.

Author: justin808

spec/react_on_rails/configuration_spec.rb

@@ -284,9 +284,9 @@ module ReactOnRails
             .with("8.2.0").and_return(true)
         end
 
-        it "defaults to :async" do
+        it "defaults to :defer" do
           ReactOnRails.configure {} # rubocop:disable Lint/EmptyBlock
-          expect(ReactOnRails.configuration.generated_component_packs_loading_strategy).to eq(:async)
+          expect(ReactOnRails.configuration.generated_component_packs_loading_strategy).to eq(:defer)
         end
 
         it "accepts :async value" do
@@ -332,10 +332,9 @@ module ReactOnRails
           allow(Rails.logger).to receive(:warn)
         end
 
-        it "defaults to :sync and logs a warning" do
+        it "defaults to :defer" do
           ReactOnRails.configure {} # rubocop:disable Lint/EmptyBlock
-          expect(ReactOnRails.configuration.generated_component_packs_loading_strategy).to eq(:sync)
-          expect(Rails.logger).to have_received(:warn).with(/does not support async script loading/)
+          expect(ReactOnRails.configuration.generated_component_packs_loading_strategy).to eq(:defer)
         end
 
         it "accepts :defer value" do