[avalanche] Fix occasional failures in abc_p2p_avalanche_voting

Summary: The test for node banning after some unexpected ava response expects no inflight poll/response, which is sometimes not true when running on qemu. Fix by finalizing/invalidating all the items along the test.

Test Plan:

./test/functional/test_runner.py abc_p2p_avalanche_voting

Also ran build-linux-aarch64, cd'ed into the build dir and ran:

for i in {1..30}; do
  echo "Trial $i" && QEMU_LD_PREFIX=/usr/aarch64-linux-gnu ./test/functional/test_runner.py abc_p2p_avalanche_voting.py || break;
done

Reviewers: #bitcoin_abc, PiRK

Reviewed By: #bitcoin_abc, PiRK

Differential Revision: https://reviews.bitcoinabc.org/D14586