[chronik] Fix chronik_plugins test

Summary: The test expects the time first seen to be identical for the txid sorting to be relevant, so there is a mock time missing.

Test Plan:

./test/functional/test_runner.py chronik_plugins

Reviewers: #bitcoin_abc, bytesofman

Reviewed By: #bitcoin_abc, bytesofman

Differential Revision: https://reviews.bitcoinabc.org/D18796