[ruby/rubygems] Move SimpleCov setup before test-unit to fix at_exit ordering

SimpleCov and test-unit both use at_exit hooks, which Ruby executes
in LIFO order. When SimpleCov was loaded after test-unit, its at_exit
hook fired first — before tests had run — producing a spurious
"Coverage report generated" message from stale results.

Moving SimpleCov setup before test-unit ensures its at_exit hook is
registered first and therefore runs last, after tests have completed.

ruby/rubygems@47e1c347e8

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: 2 people

test/rubygems/helper.rb

@@ -2,13 +2,6 @@
 
 require "rubygems"
 
-begin
-  gem "test-unit", "~> 3.0"
-rescue Gem::LoadError
-end
-
-require "test/unit"
-
 begin
   raise LoadError if ENV["GEM_COMMAND"]
 
@@ -35,6 +28,13 @@
   # SimpleCov is not installed
 end
 
+begin
+  gem "test-unit", "~> 3.0"
+rescue Gem::LoadError
+end
+
+require "test/unit"
+
 require "fileutils"
 require "pathname"
 require "pp"