Load minitest server plugin to run minitest with --bisect option

Since minitest 6 all of plug ins are opt-in, we need to load
the minitest server plug in explicitly.

Author: yahonda

activesupport/lib/active_support/testing/autorun.rb

@@ -7,4 +7,5 @@
 # be removable after the version bump, though it currently safeguards
 # against issues in environments with multiple versions installed.
 Minitest.load :rails if Minitest.respond_to? :load
+Minitest.load :server if Minitest.respond_to? :load
 Minitest.autorun