Skip a flaky test for RJIT

bootstraptest/test_thread.rb

@@ -279,6 +279,7 @@ assert_normal_exit %q{
   exec "/"
 }
 
+rjit_enabled = RUBY_DESCRIPTION.include?('+RJIT')
 assert_normal_exit %q{
   (0..10).map {
     Thread.new {
@@ -289,7 +290,7 @@ assert_normal_exit %q{
   }.each {|t|
     t.join
   }
-}
+} unless rjit_enabled # flaky
 
 assert_equal 'ok', %q{
   def m
@@ -483,7 +484,7 @@ assert_equal 'foo', %q{
   [th1, th2].each {|t| t.join }
   GC.start
   f.call.source
-} unless ENV['RUN_OPTS'] =~ /rjit/ # flaky
+} unless rjit_enabled # flaky
 assert_normal_exit %q{
   class C
     def inspect