Add and test events in pallet-conviction-voting

[rockbmb]

Description

#4613 introduced events for pallet_conviction_voting::{vote, remove_vote, remove_other_vote}.
However:

1. it did not include unlock
2. the pallet's unit tests were missing an update

Integration

N/A

Review Notes

This is as #6261 was, so it is a trivial change.

[paritytech-workflow-stopper]

All GitHub workflows were cancelled due to failure one of the required jobs.
Failed workflow url: https://github.com/paritytech/polkadot-sdk/actions/runs/11919110613
Failed job name: fmt