[rubygems/rubygems] Use `Minitest::TestTask` in a template file for `minitest`

`minitest` has introduced a rake task for running test on 5.16.0.
https://github.com/minitest/minitest/blob/master/History.rdoc#5160--2022-06-14-

This has some tasks related to running tests and it's useful for
`minitest` user I think.
https://github.com/minitest/minitest#rake-tasks-

This PR changed to use the task in a template file for `minitest`

https://github.com/rubygems/rubygems/commit/7a86d13062

lib/bundler/cli/gem.rb

@@ -11,7 +11,7 @@ module Bundler
   class CLI::Gem
     TEST_FRAMEWORK_VERSIONS = {
       "rspec" => "3.0",
-      "minitest" => "5.0",
+      "minitest" => "5.16",
       "test-unit" => "3.0",
     }.freeze
 

lib/bundler/templates/newgem/Rakefile.tt

@@ -4,13 +4,9 @@ require "bundler/gem_tasks"
 <% default_task_names = [config[:test_task]].compact -%>
 <% case config[:test] -%>
 <% when "minitest" -%>
-require "rake/testtask"
+require "minitest/test_task"
 
-Rake::TestTask.new(:test) do |t|
-  t.libs << "test"
-  t.libs << "lib"
-  t.test_files = FileList["test/**/test_*.rb"]
-end
+Minitest::TestTask.create
 
 <% when "test-unit" -%>
 require "rake/testtask"

spec/bundler/commands/newgem_spec.rb

@@ -801,13 +801,9 @@ RSpec.describe "bundle gem" do
           # frozen_string_literal: true
 
           require "bundler/gem_tasks"
-          require "rake/testtask"
+          require "minitest/test_task"
 
-          Rake::TestTask.new(:test) do |t|
-            t.libs << "test"
-            t.libs << "lib"
-            t.test_files = FileList["test/**/test_*.rb"]
-          end
+          Minitest::TestTask.create
 
           task default: :test
         RAKEFILE