[avalanche] Improve logging of the vote status update

Summary: This makes the log message consistent between blocks and proofs.

Test Plan:

ninja check-functional-extended

Run a quorum of bitcoind nodes and look at the log

Reviewers: #bitcoin_abc, PiRK

Reviewed By: #bitcoin_abc, PiRK

Subscribers: PiRK

Differential Revision: https://reviews.bitcoinabc.org/D11415