[avalanche] Check the node can mine a finalized tx

Summary: This test case was missing from the finalization functional test and will become valuable in the next preconsensus diffs.

Test Plan:

./test/functional/test_runner.py abc_p2p_avalanche_transaction_voting

Reviewers: #bitcoin_abc, PiRK

Reviewed By: #bitcoin_abc, PiRK

Differential Revision: https://reviews.bitcoinabc.org/D15779