Avoid `webpacker:install` if unnecessary

`webpacker:install` also includes execution of yarn, it takes time to execute,
so avoid unnecessary tests.

railties/lib/rails/generators/rails/plugin/plugin_generator.rb

@@ -98,6 +98,7 @@ def generate_test_dummy(force = false)
       opts[:skip_listen] = true
       opts[:skip_git] = true
       opts[:skip_turbolinks] = true
+      opts[:skip_webpack_install] = true
       opts[:dummy_app] = true
 
       invoke Rails::Generators::AppGenerator,

railties/test/generators/app_generator_test.rb

@@ -113,7 +113,7 @@ def test_skip_bundle
   end
 
   def test_assets
-    run_generator [destination_root, "--no-skip-javascript"]
+    run_generator [destination_root, "--no-skip-javascript", "--skip-webpack-install"]
 
     assert_file("app/views/layouts/application.html.erb", /stylesheet_link_tag\s+'application', media: 'all', 'data-turbolinks-track': 'reload'/)
     assert_file("app/views/layouts/application.html.erb", /javascript_pack_tag\s+'application', 'data-turbolinks-track': 'reload'/)
@@ -840,7 +840,7 @@ def test_skip_webpack_install
   end
 
   def test_generator_if_skip_turbolinks_is_given
-    run_generator [destination_root, "--skip-turbolinks", "--no-skip-javascript"]
+    run_generator [destination_root, "--skip-turbolinks", "--no-skip-javascript", "--skip-webpack-install"]
 
     assert_no_gem "turbolinks"
     assert_file "app/views/layouts/application.html.erb" do |content|

railties/test/generators/shared_generator_tests.rb

@@ -27,7 +27,7 @@ def application_path
   end
 
   def test_skeleton_is_created
-    run_generator [destination_root, "--no-skip-javascript"]
+    run_generator [destination_root, "--no-skip-javascript", "--skip-webpack-install"]
 
     default_files.each { |path| assert_file path }
   end
@@ -196,7 +196,7 @@ def test_generator_if_skip_active_record_is_given
   end
 
   def test_generator_for_active_storage
-    run_generator [destination_root, "--no-skip-javascript"]
+    run_generator [destination_root, "--no-skip-javascript", "--skip-webpack-install"]
 
     unless generator_class.name == "Rails::Generators::PluginGenerator"
       assert_file "#{application_path}/app/javascript/packs/application.js" do |content|
@@ -226,7 +226,7 @@ def test_generator_for_active_storage
   end
 
   def test_generator_if_skip_active_storage_is_given
-    run_generator [destination_root, "--skip-active-storage", "--no-skip-javascript"]
+    run_generator [destination_root, "--skip-active-storage", "--no-skip-javascript", "--skip-webpack-install"]
 
     assert_file "#{application_path}/config/application.rb", /#\s+require\s+["']active_storage\/engine["']/
 
@@ -256,7 +256,7 @@ def test_generator_if_skip_active_storage_is_given
   end
 
   def test_generator_does_not_generate_active_storage_contents_if_skip_active_record_is_given
-    run_generator [destination_root, "--skip-active-record", "--no-skip-javascript"]
+    run_generator [destination_root, "--skip-active-record", "--no-skip-javascript", "--skip-webpack-install"]
 
     assert_file "#{application_path}/config/application.rb", /#\s+require\s+["']active_storage\/engine["']/