Some global variables can be accessed from ractors

Some global variables should be used from non-main Ractors.
[Bug #17268]

```ruby
     # ractor-local (derived from created ractor): debug
     '$DEBUG' => $DEBUG,
     '$-d' => $-d,

     # ractor-local (derived from created ractor): verbose
     '$VERBOSE' => $VERBOSE,
     '$-w' => $-w,
     '$-W' => $-W,
     '$-v' => $-v,

     # process-local (readonly): other commandline parameters
     '$-p' => $-p,
     '$-l' => $-l,
     '$-a' => $-a,

     # process-local (readonly): getpid
     '$$'  => $$,

     # thread local: process result
     '$?'  => $?,

     # scope local: match
     '$~'  => $~.inspect,
     '$&'  => $&,
     '$`'  => $`,
     '$\''  => $',
     '$+'  => $+,
     '$1'  => $1,

     # scope local: last line
     '$_' => $_,

     # scope local: last backtrace
     '$@' => $@,
     '$!' => $!,

     # ractor local: stdin, out, err
     '$stdin'  => $stdin.inspect,
     '$stdout' => $stdout.inspect,
     '$stderr' => $stderr.inspect,
```

1 files changed, 3 insertions, 0 deletions

diff --git a/io.c b/io.c
index c986ffbc47..3b4ae6d60b 100644
--- a/io.c
+++ b/io.c
@@ -13543,6 +13543,7 @@ Init_IO(void)
     rb_define_hooked_variable("$\\", &rb_output_rs, 0, deprecated_str_setter);
 
     rb_define_virtual_variable("$_", get_LAST_READ_LINE, set_LAST_READ_LINE);
+    rb_gvar_ractor_local("$_");
 
     rb_define_method(rb_cIO, "initialize_copy", rb_io_init_copy, 1);
     rb_define_method(rb_cIO, "reopen", rb_io_reopen, -1);
@@ -13764,6 +13765,8 @@ Init_IO(void)
     ARGF.filename = rb_str_new2("-");
 
     rb_define_hooked_variable("$-i", &argf, opt_i_get, opt_i_set);
+    rb_gvar_ractor_local("$-i");
+
     rb_define_hooked_variable("$*", &argf, argf_argv_getter, rb_gvar_readonly_setter);
 
 #if defined (_WIN32) || defined(__CYGWIN__)