Improve compatibility between Logger and ActiveSupport::BroadcastLogger

The usage of `dispatch` in all logging methods causes common usages such
as `logger.info` to return an array of loggers, making it unsafe for an
application to upgrade to Rails 7.1.

Returning `nil` is more efficient, and is the default behavior when
using `Logger`.

Author: ElMassimo

activesupport/test/broadcast_logger_test.rb

@@ -302,7 +302,7 @@ def info(msg, &block)
       assert_same logger, broadcast_logger.broadcasts.sole
     end
 
-    test "logging has no return value" do
+    test "logging always returns true" do
       assert_equal true, @logger.info("Hello")
       assert_equal true, @logger.error("Hello")
     end