Remove ibf_dumper's WB_PROTECTED status

It doesn't have the right write barriers in place. For example, there is

    rb_mark_set(dump->global_buffer.obj_table);

in the mark function, but there is no corresponding write barrier when
adding to the table in the
`ibf_dump_object() -> ibf_table_find_or_insert() -> st_insert()` code path.

To insert write barrier correctly, we need to store the T_STRUCT VALUE
inside `struct ibf_dump`. Instead of doing that, let's just demote it
to WB unproected for correctness. These dumper object are ephemeral so
there is not a huge benefit for having them WB protected.

Users of the bootsnap gem ran into crashes due to this issue:
Shopify/bootsnap#436

Fixes [Bug #19419]

compile.c

@@ -13056,7 +13056,7 @@ ibf_dump_memsize(const void *ptr)
 static const rb_data_type_t ibf_dump_type = {
     "ibf_dump",
     {ibf_dump_mark, ibf_dump_free, ibf_dump_memsize,},
-    0, 0, RUBY_TYPED_WB_PROTECTED | RUBY_TYPED_FREE_IMMEDIATELY
+    0, 0, RUBY_TYPED_FREE_IMMEDIATELY
 };
 
 static void