[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