DEV: Don’t replace Rails logger in specs (#29721)

Instead of replacing the Rails logger in specs, we can instead use
`#broadcast_to` which has been introduced in Rails 7.

spec/rails_helper.rb

@@ -967,12 +967,12 @@ ensure
 end
 
 def track_log_messages
-  old_logger = Rails.logger
-  logger = Rails.logger = FakeLogger.new
+  logger = FakeLogger.new
+  Rails.logger.broadcast_to(logger)
   yield logger
   logger
 ensure
-  Rails.logger = old_logger
+  Rails.logger.stop_broadcasting_to(logger)
 end
 
 # this takes a string and returns a copy where 2 different