Some callable method entries (cme) can be a key of `overloaded_cme_table` and the keys should be pinned because the table is numtable (VALUE is a key). Before the GC checks the cme is in `overloaded_cme_table` by looking up the table, but it needs VM locking. It works well in normal GC marking because it is protected by the VM lock, but it doesn't work on `rb_objspace_reachable_objects_from` because it doesn't use VM lock. Now, the number of target cmes are small enough, I decide to pin down all possible cmes instead of using looking up the table.