Suppress RuboCop output when there are no offenses in code generation

Follow up rails#51782.

> But it's overkill for the default case where people use the default style guide,
> and it introduces both delay and console output as a cost.

When there are no offenses with the coding style generated by code generation,
outputting RuboCop results to the console was redundant.
Since RuboCop has `--format=quiet` option that suppresses console output
when there are no offenses, this PR adds that option:
https://docs.rubocop.org/rubocop/1.63/formatters.html#quiet-formatter

While this PR doesn't resolve any added execution speed by RuboCop,
the frequency of using the generator is not high within the development flow.
Therefore, depending on the execution speed, it might be possible to uncomment rails#51782,
but this PR respects the defaults in rails#51782 and doesn't address that.

Author: koic

railties/lib/rails/configuration.rb

@@ -135,7 +135,7 @@ def apply_rubocop_autocorrect_after_generate!
         after_generate do |files|
           parsable_files = files.filter { |file| File.exist?(file) && file.end_with?(".rb") }
           unless parsable_files.empty?
-            system(RbConfig.ruby, "bin/rubocop", "-A", "--fail-level=E", *parsable_files, exception: true)
+            system(RbConfig.ruby, "bin/rubocop", "-A", "--fail-level=E", "--format=quiet", *parsable_files, exception: true)
           end
         end
       end

railties/test/application/generators_test.rb

@@ -263,7 +263,7 @@ def check_expected
         end
 
         output = rails("generate", "model", "post", "title:string", "body:string")
-        assert_match(/3 files inspected, no offenses detected/, output)
+        assert_no_match(/3 files inspected, no offenses detected/, output)
       end
 
       test "generators with apply_rubocop_autocorrect_after_generate! and pretend" do