suppress warning introduced by r42439 [ruby-dev:47040]

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@42453 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

test/coverage/test_coverage.rb

@@ -47,7 +47,7 @@ class TestCoverage < Test::Unit::TestCase
     Dir.mktmpdir {|tmp|
       Dir.chdir(tmp) {
         File.open("test.rb", "w") do |f|
-          f.puts "1\n" * 10000
+          f.puts "__id__\n" * 10000
           f.puts "def ignore(x); end"
           f.puts "ignore([1"
           f.puts "])"