[avalanche] Improve test coverage of existing parking behavior
Summary:
Generalize the test coverage of parking blocks near the chaintip so that we
check different chain lengths.
Depends on D12943
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/D12944