[avalanche] Select the favorite orphan in case of a conflict during a rescan

Summary:
This is a follow-up to D10524, apply the same rule for the proofs newly orphaned after a new block is mined.

Ref T1854.

Depends on D10524.

Test Plan:

ninja check-avalanche

Reviewers: #bitcoin_abc, deadalnix

Reviewed By: #bitcoin_abc, deadalnix

Maniphest Tasks: T1854

Differential Revision: https://reviews.bitcoinabc.org/D10661