Update dependency minitest to v6

Author: renovate[bot]

Gemfile

@@ -129,7 +129,7 @@ group :test do
   # Use system testing [https://guides.rubyonrails.org/testing.html#system-testing]
   gem 'capybara'
   gem 'climate_control'
-  gem 'minitest', '< 6'
+  gem 'minitest', '< 7'
   gem 'mocha'
   gem 'selenium-webdriver'
   gem 'simplecov'

Gemfile.lock

@@ -234,7 +234,8 @@ GEM
     marcel (1.1.0)
     matrix (0.4.2)
     mini_mime (1.1.5)
-    minitest (5.27.0)
+    minitest (6.0.1)
+      prism (~> 1.5)
     mocha (3.0.1)
       ruby2_keywords (>= 0.0.5)
     msgpack (1.8.0)
@@ -529,7 +530,7 @@ DEPENDENCIES
   http
   importmap-rails
   jbuilder
-  minitest (< 6)
+  minitest (< 7)
   mitlibraries-theme!
   mocha
   omniauth