test: add logging for mining_getblocktemplate_longpoll.py

Summary:
This is a backport of core#20159 [3/3]
https://github.com/bitcoin/bitcoin/pull/20159/commits/b128b566725a5037fdaea99940d1b9de5553d198

Depends on D10518

Test Plan: test/functional/test_runner.py mining_getblocktemplate_longpoll

Reviewers: #bitcoin_abc, Fabien

Reviewed By: #bitcoin_abc, Fabien

Differential Revision: https://reviews.bitcoinabc.org/D10519