[Solved by 1.x] Cannot use resumption PSK from the current epoch

[mulmarta]

This is just to keep track of a known issue that will become no-issue after GroupStateStorage is removed in 1.x:

Calling group.commit_builder()?.add_resumption_psk_for_group(current_epoch, another_group_id) will cause an error "PSK not found" because we only search for resumption PSKs in past epochs, not the current group state.