Naming of region attribute table accessors is a bit lacking: there should be a difference between overwriting the entire region attribute table contents and just updating fields

Also, since JDK-8343782 we do select old gen groups with pinned regions into the collection set, but the following comment states otherwise:

  void set_in_old(uintptr_t index, bool remset_is_tracked) {
    assert(get_by_index(index).is_default(),
           "Region attributes at index " INTPTR_FORMAT " should be default but is %s", index, get_by_index(index).get_type_str());
    // We do not select regions with pinned objects into the collection set.
    const bool region_is_pinned = false;
    set_by_index(index, G1HeapRegionAttr(G1HeapRegionAttr::Old, remset_is_tracked, region_is_pinned));
  }

Fix the comment.

(Later in the pre-evacuate collection set phase we fix up both flags another time)