Fix wrong GENIV WB on too_complex Ractor traversal

WBCHECK ERROR: Missed write barrier detected!
      Parent object: 0x7c4a5f1f66c0 (wb_protected: true)
        rb_obj_info_dump: 0x00007c4a5f1f66c0 T_IMEMO/<fields>
      Reference counts - snapshot: 2, writebarrier: 0, current: 2, missed: 1
      Missing reference to: 0x7b6a5f2f7010
        rb_obj_info_dump: 0x00007b6a5f2f7010 T_ARRAY/Array [E ] len: 1 (embed)

bootstraptest/test_ractor.rb

@@ -1923,6 +1923,60 @@ assert_equal 'ok', %q{
   roundtripped_obj.instance_variable_get(:@array) == [1] ? :ok : roundtripped_obj
 }
 
+# move object with many generic ivars
+assert_equal 'ok', %q{
+  ractor = Ractor.new { Ractor.receive }
+  obj = Array.new(10, 42)
+  0.upto(300) do |i|
+    obj.instance_variable_set(:"@array#{i}", [i])
+  end
+
+  ractor.send(obj, move: true)
+  roundtripped_obj = ractor.value
+  roundtripped_obj.instance_variable_get(:@array1) == [1] ? :ok : roundtripped_obj
+}
+
+# move object with complex generic ivars
+assert_equal 'ok', %q{
+  # Make Array too_complex
+  30.times { |i| [].instance_variable_set(:"@complex#{i}", 1) }
+
+  ractor = Ractor.new { Ractor.receive }
+  obj = Array.new(10, 42)
+  obj.instance_variable_set(:@array1, [1])
+
+  ractor.send(obj, move: true)
+  roundtripped_obj = ractor.value
+  roundtripped_obj.instance_variable_get(:@array1) == [1] ? :ok : roundtripped_obj
+}
+
+# copy object with complex generic ivars
+assert_equal 'ok', %q{
+  # Make Array too_complex
+  30.times { |i| [].instance_variable_set(:"@complex#{i}", 1) }
+
+  ractor = Ractor.new { Ractor.receive }
+  obj = Array.new(10, 42)
+  obj.instance_variable_set(:@array1, [1])
+
+  ractor.send(obj)
+  roundtripped_obj = ractor.value
+  roundtripped_obj.instance_variable_get(:@array1) == [1] ? :ok : roundtripped_obj
+}
+
+# copy object with many generic ivars
+assert_equal 'ok', %q{
+  ractor = Ractor.new { Ractor.receive }
+  obj = Array.new(10, 42)
+  0.upto(300) do |i|
+    obj.instance_variable_set(:"@array#{i}", [i])
+  end
+
+  ractor.send(obj)
+  roundtripped_obj = ractor.value
+  roundtripped_obj.instance_variable_get(:@array1) == [1] ? :ok : roundtripped_obj
+}
+
 # moved composite types move their non-shareable parts properly
 assert_equal 'ok', %q{
   k, v = String.new("key"), String.new("value")

ractor.c

@@ -1667,7 +1667,7 @@ obj_traverse_replace_i(VALUE obj, struct obj_traverse_replace_data *data)
             struct obj_traverse_replace_callback_data d = {
                 .stop = false,
                 .data = data,
-                .src = obj,
+                .src = fields_obj,
             };
             rb_st_foreach_with_replace(
                 rb_imemo_fields_complex_tbl(fields_obj),