[Backport #21638] Mark ractor-local $VERBOSE and $DEBUG

https://github.com/sampersand/blog/blob/master/the%20-s%20flag.md#the-segfault

Author: nobu

ractor.c

@@ -217,6 +217,8 @@ ractor_mark(void *ptr)
     rb_gc_mark(r->r_stdin);
     rb_gc_mark(r->r_stdout);
     rb_gc_mark(r->r_stderr);
+    rb_gc_mark(r->verbose);
+    rb_gc_mark(r->debug);
     rb_hook_list_mark(&r->pub.hooks);
 
     if (r->threads.cnt > 0) {

test/ruby/test_rubyoptions.rb

@@ -573,6 +573,8 @@ def test_sflag
 
     assert_in_out_err(%w(- -#=foo), "#!ruby -s\n", [],
                       /invalid name for global variable - -# \(NameError\)/)
+
+    assert_in_out_err(['-s', '-e', 'GC.start; p $DEBUG', '--', '-DEBUG=x'], "", ['"x"'])
   end
 
   def test_option_missing_argument