Upgrade minitest 5.27.0 to minitest 6.0.1 for Rails 8.1

This upgrade is now possible because Rails 8.1.2 added support for Minitest 6. Even Rails 8.0.x now supports Minitest 6 but currently only in 8-0-stable branch as there hasn't been a release yet.

Author: larouxn

Gemfile

@@ -7,7 +7,15 @@ gemspec
 CURRENT_RAILS_VERSION = "8.1"
 rails_version = ENV.fetch("RAILS_VERSION", CURRENT_RAILS_VERSION)
 
-gem "minitest", "< 6.0" # Rails 8.1.1 doesn't support minitest 6.0 which causes errors
+# Rails main and 8.1.2 onward support Minitest 6.
+# Rails 8.0.x lacks support for Minitest 6 in released versions.
+# TODO: Remove conditional once a Rails 8.0.x release with Minitest 6 support is cut.
+# See: https://github.com/rails/rails/commit/ec62932ee7d31e0ef870e61c2d7de2c3efe3faa6
+if rails_version == "8.0"
+  gem "minitest", "< 6"
+else
+  gem "minitest"
+end
 gem "minitest-hooks"
 gem "minitest-reporters"
 gem "debug"

Gemfile.lock

@@ -214,7 +214,8 @@ GEM
       net-smtp
     marcel (1.1.0)
     mini_mime (1.1.5)
-    minitest (5.27.0)
+    minitest (6.0.1)
+      prism (~> 1.5)
     minitest-hooks (1.5.3)
       minitest (> 5.3)
     minitest-reporters (1.7.1)
@@ -443,7 +444,7 @@ DEPENDENCIES
   json_api_client!
   kramdown (~> 2.5)
   kredis
-  minitest (< 6.0)
+  minitest
   minitest-hooks
   minitest-reporters
   mutex_m