Silence coverage report output from coverage:report task

The collate run printed a "Coverage report generated for ..." line
listing every per-process command name after each test/spec run. Mirror
the stdout redirection already used in spec_helper's SimpleCov at_exit
hook so the HTML report is still written without the noisy summary.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

Author: hsbt

Rakefile

@@ -136,6 +136,7 @@ task "coverage:report" do
     next
   end
 
+  $stdout = File.open(File::NULL, "w")
   SimpleCov.collate Dir[resultset] do
     coverage_dir "coverage"
     add_filter "/test/"
@@ -153,6 +154,8 @@ task "coverage:report" do
       src.filename.include?("/lib/bundler/") || src.filename.end_with?("/lib/bundler.rb")
     end
   end
+ensure
+  $stdout = STDOUT
 end
 
 spec = Gem::Specification.load(File.expand_path("rubygems-update.gemspec", __dir__))