[chronik] Add a test for invalidated blocks on a parked chain

Summary: When a block connects on a parked chain, it gets invalidated as expected but chronik should not send a websocket message in this case: it's basically another chain at this point.

Test Plan:

./test/functional/test_runner.py chronik_ws

Reviewers: #bitcoin_abc, PiRK

Reviewed By: #bitcoin_abc, PiRK

Subscribers: PiRK

Differential Revision: https://reviews.bitcoinabc.org/D16889