Ractor.shareable_proc(&pr) should copy pr

`pr` should not change on this method.

Author: ko1

bootstraptest/test_ractor.rb

@@ -157,6 +157,16 @@
   Ractor.shareable_proc(&closure).call
 }
 
+# Ractor.make_shareable makes a copy of given Proc
+assert_equal '[true, true]', %q{
+  pr1 = Proc.new do
+    self
+  end
+  pr2 = Ractor.shareable_proc(&pr1)
+
+  [pr1.call == self, pr2.call == nil]
+}
+
 # Ractor::IsolationError cases
 assert_equal '3', %q{
   ok = 0

ractor.c

@@ -2376,7 +2376,7 @@ ractor_shareable_proc(rb_execution_context_t *ec, VALUE replace_self, bool is_la
     }
     else {
         VALUE proc = is_lambda ? rb_block_lambda() : rb_block_proc();
-        return rb_proc_ractor_make_shareable(proc, replace_self);
+        return rb_proc_ractor_make_shareable(rb_proc_dup(proc), replace_self);
     }
 }