[avalanche] Add test coverage for parking against avalanche finalized chaintip
Summary:
Ensure we do not introduce regressions related to parking blocks near the chaintip.
With avalanche now enabled by default and validation changes planned, testing this
behavior explicitly is very important.
Test Plan:
ninja ./test/functional/test_runner.py abc_p2p_avalanche_voting
Reviewers: #bitcoin_abc, Fabien
Reviewed By: #bitcoin_abc, Fabien
Subscribers: Fabien
Differential Revision: https://reviews.bitcoinabc.org/D12943